Everyday Practical Electronics 2000-11 - PDF Free Download (2024)

Everyday Practical Electronics, November 2000

which even the in-built error-trapping might not intercept!

OTHER CHANGES

Minor cosmetic changes in Toolkit’s program may be spotted, but nothing worth highlighting. Special thanks to Andy Flind for his help with regard to INCLUDE files. If you would like to suggest further improvements to this software, let us know at Editorial (the author might even add them – one rainy day!)

REMINDER

When sending a .OBJ file to a PIC, Toolkit (and its predecessors) automatically places GOTO 5 in location 0 (the Reset vector), followed by NOP into locations 1, 2 and 3. This action is specified by PTASM$ in source code file TKMAIN02.BAS, in which “CHR$(40) + CHR$(5)” specifies the jump to location 5. Location 4 holds the Interrupt vector, which is specified by the user in the PIC source code (.ASM). It is the first .ORG that the code is allowed to specify and must always be stated as .ORG 4. Location 5 is that at which the program itself commences, as previously stated by the GOTO 5 command in location 0. The logic behind this format is historical, mandatory and originally instigated in the Simple PIC16C84 Programmer of Feb ’96. It has been highlighted on several occasions since then. $

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INVERTERS

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Everyday Practical Electronics, November 2000

SURFING THE INTERNET

NET WORK ALAN WINSTANLEY AltaVista Cashes Out

March 2000, AltaVista shook the UK Internet dial-up market by announcing its intention to offer a fixed price unmetered access for home users, as reported in May 2000 Net Work. In order to ensure that the service wouldn’t be over-subscribed, AltaVista’s intention was to roll out at a rate of 90,000 users per month. This was a surprising and ill-conceived move, given that other ISPs had tried and failed to offer an unmetered service, often blaming over-subscription or over-use by consumers. However, AltaVista did succeed in wrong-footing cable operator ntl to offer its own unmetered service, and BT too was forced onto the defensive. There have been numerous complaints concerning ntl’s failure to cope with the demand, resulting in delays of months for some subscribers. Several companies including LineOne and CallNet0800 have since scrapped unmetered access because it is commercially unsustainable. The free service 08004U also folded, its owners EZESURF reportedly blaming its supplier, Planet Online, for billing errors that resulted in Planet Online (now Energis Squared) bankrupting EZESURF with an unexpected bill for call charges totalling £1.7 million. The countdown to the launch of AltaVista UK’s unmetered service soon began. Their upbeat on-line FAQs talked about providing “starter kits’’ to Windows users, also stating that AV was introducing this new service to “remove the uncertainty of open-ended access call charges’’. They were “on track’’ to launch sometime in June. On August 3, AltaVista E-mailed interested subscribers to announce that on June 30 it had indeed launched its new service which “is currently being rolled out to our list of pre-registered customers’’ and to prevent over-subscription this would happen “in a controlled manner.’’ This would, in the event, mean “in your dreams.’’ Things started to smell fishy when at the same time AltaVista launched two additional subscriber services called Net on Demand and Freetime 20. Meantime, a nationwide appeal by the UK press failed to produce any users of AltaVista’s new unmetered service at all. The rest is history – there never actually was an unmetered service from AltaVista UK. British Telecom accused them of turning reality on its head and Andy Mitchell, AltaVista’s UK Managing Director resigned in disgrace over the affair. AltaVista could never have made their unmetered service work, and it is for a good reason that AltaVista FreeAccess in the USA and Canada (see www.microav.com) is actually supported by on-line advertising delivered to your desktop.

I

N EARLY

Sense of déjà vu

There is a sense of déjà vu about unmetered access. As a rule, people will often stay online and consume bandwidth for no reason at all, except that it is cheap. Way back in the early 1990’s London-based Demon Internet offered dial-up Internet access through a number of points of presence (PoPs) dotted across the UK. You dialled the nearest one in order to obtain local rate calls, and getting through within ten or twenty attempts was akin to winning the lottery. A small number of canny users in the city of Hull, which enjoys its own independent telephone service including cheap all-day local calls, soon found that they could dial into the Internet using Demon’s Hull PoP, and by hogging the line they could enjoy a leased line to the Internet for just a few pence a day. Needless to say, the Hull PoP was soon relocated out of the city. Always-on Internet access is still something of a luxury in this country. Cable company ntl will automatically cut off subscribers

Everyday Practical Electronics, November 2000

every two hours regardless, and will time out after five minutes of inactivity. Always-on access would be nice to have, but how many people seriously need it? It eats precious bandwidth and opens your vulnerable system to the possibility of hacking or nuking, so you face the prospect of configuring firewall software such as Norton Internet Security, Nukenabber or the highly regarded ZoneAlarm software. Always-on broadband services (ADSL) are on the way to enabling consumers to download material at 512Kbps or more, which judging by BT’s Openworld data seems to be good for adding a streaming video content to your Internet experience and not much more: in reality, rare is the time most people need massive bandwidth to download huge multi-megabyte files. BT Openworld supports most Internet protocols but there are exceptions, including H.323-based applications, Microsoft Netmeeting and ICQ. It’s time to fire up the modem again. Not everyone will be able to receive ADSL due to their location or availability from the local exchange, and most people will not want to pay £39.99 per month ($58) and £150 ($217) installation for it either. Reader Per Gradal in Sweden tells me that ADSL provided via Telia costs SKr. 200 per month (say £15 or $22) and SKr. 1200 (£90 or $130) installation, with unlimited download, and you can quit within a month. BT ADSL easily costs more than double this. The Swedish Government, Per says, hopes to give the entire population broadband access before 2004.

V.92 Modems

One advantage of ISDN2e is the near immediacy of connecting to the Internet, typically within four seconds or so. Coupled with the provision of two digital and two analogue ports (use any two at a time) and the faster download speeds, ISDN2e starts to sound more appealing. If, like myself, you waste a total of three hours a month waiting for your modem to connect, and you are teetering on the brink of installing ISDN, then just when you think there is no life after V.90 (56K) modems, along comes another standard to give you hope. The new V.92 modem standard agreed by the ITU in July 2000 doesn’t increase the download speed beyond the existing 56K (V.90) rate, but it does increase the upload rate to the Internet from 33·6Kbps to about 48Kbps maximum. More importantly (for me, anyway), V.92 promises to vastly reduce the negotiation time needed when connecting to the Internet – as little as ten seconds – and ISPs will benefit from freeing up the bandwidth to the modem racks. What will be the best news of all for many users, V.92 also offers a new feature dubbed “modem on hold’’. If your modem is on-line and that same telephone line should happen to receive an incoming phone call, then instead of the modem causing an engaged tone, it will put the Internet call on hold for a period determined by the ISP, and allow the incoming call to be handled by the user. Modem software may possibly issue a warning when the timeout period is approaching, but even if you lose the call, you benefit from fast re-dial periods afterwards. V.92 could be a genuine money-saver: some consumers may be able to cancel Call Waiting service costs on that line, or even cancel the rental on a second line altogether. Don’t get too excited just yet though. As always, the improved standard depends on ISPs updating their modem racks and software. Watch out for a whole slew of new V.92 modems appearing by the end of the year, and also be sure to check modem web sites to see whether your flash-upgradeable modem can be upgraded. The telephone line and analogue modem will be with us for many years to come yet. You can E-mail me at [emailprotected]. See you next month.

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Special Series

THE SCHMITT TRIGGER

OUTPUT VOLTAGE VOUT

VOUT (HIGH)

VIN INCREASING

VIN DECREASING

VOUT (LOW)

HYSTERESIS VOLTAGE VH INPUT VOLTAGE VIN VTU

VTL

ANTHONY H. SMITH

Part 1

In this new short series, we will investigate the Schmitt trigger’s operation; explore the various ways of implementing its special characteristics and also look at how we can use it to create oscillators and pulse width modulators.

Discrete Schmitt triggers based on bipolar transistors N 1938, the Journal of Scientific Instruments published details of

I

a comparator circuit that converted a slowly varying input signal into an abrupt change in output voltage. Based on cross-coupled thermionic valves, the circuit was developed by one O. H. Schmitt, and since then the term “Schmitt trigger’’ has been used to describe a particular type of circuit in which positive feedback is used to enhance the switching action of a comparator. In this series of articles, we’ll investigate the Schmitt trigger’s operation, and examine different ways of implementing the function using transistors, operational amplifiers (op.amps) and digital gates. Also, we will look at ways in which the circuit can be improved and adapted to create other functions such as oscillators and pulse width modulators.

Thresholds and Hysteresis

VCC (+5V)

TRANSISTOR CONNECTIONS (BOTTOM VIEW) b e

R1

VC2 (VOUT)

BC108B

VC1

C1 100n

c ZTX314 c b e

R3

IC2

IC1

RSOURCE

TR1 IB1 b

c

c

b

R4 IB2

e

e

VBE1

VIN

TR2

VBE2

VB1

IE VE

R2

VB2

R5 0V

Essentially, the Schmitt trigger can be considered as a voltage comparator with two distinct thresholds, an “upper’’ threshold and a “lower’’ threshold, where the value of each threshold is deterFig.1.1. Simple two-transistor Schmitt trigger circuit based on mined by positive feedback from the output. The voltage difference a differential “long-tailed’’ pair set-up. between thresholds is termed the “hysteresis’’. (See panel What is Hysteresis?). “off’. Transistor TR1 is now responsible for all the emitter curA simple differential amplifier consisting of bipolar transistors rent, IE, flowing in resistor R2, and since TR2’s collector current TR1 and TR2 connected as a “long-tailed pair’, where the emitter is zero there is no voltage drop across resistor R3 and VC2 rises resistor R2, common to both devices, forms the “tail’’, is shown in to VCC. Note how VB2 effectively forms a reference level, or Fig.1.1. For the moment, assume that resistor R4 is disconnected threshold: once VB1 crosses this threshold, the circuit “changes from TR1’s collector (c) and instead is connected to the positive state’’ as shown by the transition in VC2. The circuit behaves as supply rail, VCC, such that TR2’s base (b) is held at a constant volta comparator, where VB1 is “compared’’ to the VB2 reference age, VB2, determined by the potential divider effect of resistors R4 level. and R5. An ideal case where VB1 is completely free of any “noise’, If TR1’s base voltage, VB1, is lower than VB2, TR1 will be “off’’ such that VC2 makes a clean transition as transistors TR1 and and TR2 will be conducting, such that the emitter potential, VE, TR2 turn on and off, respectively is shown in Fig.1.2a. In praccommon to both transistors, will equal VB2 – VBE2, where VBE2 is the tice, however, all real-world signals are “corrupted’’ by some base-emitter potential of TR2. Since TR1 is “off’, no current flows degree of noise as shown in Fig.1.2b, where the noise on TR1’s through resistor R1, and TR1’s collector voltage, VC1, equals VCC. base voltage causes the signal to cross the VB2 threshold not However, since transistor TR2 is conducting, its collector current, once, but three times, resulting in an unwanted “pulse’’ in TR2’s IC2, will cause a voltage drop across resistor R3 such that its colleccollector signal. If the comparator were being used as the input tor potential, VC2, will be lower than VCC. The actual value of VC2 stage of, say, a digital counter, each of these pulses would result will depend on the relative values of resistors R2 and R3, and on in an extra “count’’ – clearly an erroneous and unacceptable TR2’s base voltage, VB2. condition. If we now increase VB1 by applying a linearly increasing input voltage, VIN, the point will come where VB1 equals VB2: this is A) B) shown in the graph of Fig.1.2a. If the transisVB1=VB2 tors are matched (i.e., if they have identical VB2 VB2 characteristics), the base-emitter junction of VB1 WITH NOISE CROSSES "NOISELESS" VB1 TR1 will now be sufficiently forward biased SUPERIMPOSED THRESHOLD THREE NOISE TIMES CAUSING to enable it to conduct, and its collector potenUNWANTED PULSE IN VC2 tial will fall due to current IC1 now flowing VCC VCC VC2 VC2 through resistor R1. Further small increases in VB1 cause corTIME TIME responding increases in the emitter potential, VE, and, since VB2 is fixed at a constant Fig.1.2. The performance of a simple comparator is degraded by noise. level, VBE2 starts to decrease and TR2 turns

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Everyday Practical Electronics, November 2000

Positive Thinking How, then, do we eliminate the effects of noise? One solution is to remove, or filter out, the noise before it reaches transistor TR1’s base. However, if the noise content is relatively large, or if it is similar in frequency to the wanted signal, the degree of filtering required may be impractical. Furthermore, all filters introduce a “phase delay’’ to the signal which may be unacceptable in certain applications. The solution is to introduce a specific amount of positive feedback. Let us now disconnect resistor R4 from VCC and reconnect it to TR1’s collector as shown in Fig.1.1. If we assume that VB1 is small such that TR1 is off, TR2’s base potential, VB2 will be set by the potential divider formed by resistors R1, R4 and R5. Since TR1 is off, IC1 is zero and has no effect on VB2. As the input voltage VIN increases, we arrive at the point where

VB1 just exceeds VB2 and, as before, transistor TR1 now starts to conduct, and as its collector voltage starts to fall it “pulls down’’VB2 to a lower level. This, in turn, lowers the common emitter potential, VE, which increases TR1’s base-emitter potential, VBE1, and causes it to conduct even harder. This regenerative process has two beneficial effects. First, it causes the transistors to switch on and off much more rapidly than for the case of the simple comparator. Second, it imparts a significant amount of noise immunity to the comparator action. This can be seen in the graph of Fig.1.6, where VB2 is initially at its higher level, denoted VTU for “upper threshold’. When VB1 crosses this threshold, transistor TR1 turns on and, if resistor R1 is several times larger than R2, TR1 will saturate causing VB2 to fall to a lower, constant level denoted VTL for “lower threshold’. The difference between VTU and VTL is the hysteresis voltage, VH. Provided VH is large enough, the noise superimposed on VB1

WHAT IS HYSTERESIS? Whilst using a garden tap the other day, a negative residual flux density. An increase FLUX DENSITY, B it was noticed that it needed quite a few in magnetising force then causes the curve (TESLA) A turns before the water started to flow. to follow path E to F and then F to A. However, in order to stop the flow, at least The resulting symmetrical curve shows B four clockwise turns were needed before how the flux density always “lags behind’’ the water stopped. The difference between the magnetising force: the Collins English C “flow’’ and “no flow’’ – in this case four turns Dictionary defines hysteresis as “the time O F MAGNETISING – is an example of hysteresis. lag of magnetism behind the magnetising FORCE, H In this example, the hysteresis served no force’’, where hysteresis is derived from the (AMPERES/METRE) E useful purpose, but in other “on-off’’ control Greek word hysterein meaning “to lag applications, hysteresis is essential to behind’’. D avoid the over-frequent cycling of pumps, Schmitt trigger circuits like the ones motors, heaters, and so on. Perhaps the described in this article also exhibit hysteremost obvious example is the thermostatic sis, but this time the relationship is between control used in domestic central heating Fig.1.3. Typical BH-curve for mild steel. input voltage and output voltage. Fig.1.4 systems. shows the hysteresis curve for the nonIf the room thermostat is set to, say, 20°C, the heating will inverting Schmitt triggers of Fig.1.1 and Fig.1.10. Initially, when remain on until the room temperature rises to around 22°C where input VIN is a minimum, the output voltage is at its minimum level, it turns off. However, if the room temperature falls a fraction of a VOUT(LOW), and remains there until VIN has increased to the upper degree below 22°C, the heating does not come back on again but threshold voltage, VTU, at which point VOUT makes a rapid transiremains off until the temperature drops to 20°C. tion to its maximum level, VOUT(HIGH). Any further increase in VIN has The difference, or hysteresis, of 2°C provides a “time lag’’ no effect on VOUT. during which the room gradually heats up and cools down. As VIN is reduced, VOUT remains at its maximum level until VIN Without the hysteresis, the heating would continually cycle on falls to the lower threshold voltage, VTL, where VOUT rapidly falls and off as the temperature varied a fraction below and above back to its minimum level, VOUT(LOW). The “width’’ of the loop is the the set point. hysteresis voltage, VH, which is simply the difference between VTU Hysteresis is also found naturally, a good example being the soand VTL, that is: called “BH curve’’ of a magnetic material, which defines the VH = VTU – VTL. Notice how the curve follows an “anti-clockwise’’ relationship between the Magnetising Force, H, applied to the path around the loop. material and the resulting Flux Density, B. An example of a “clockwise’’ hysteresis loop is shown in Fig.1.5 A typical BH curve for mild steel is shown in Fig.1.3. Gradually which represents the input-output relationship for inverting Schmitt increasing the magnetising force from zero causes the curve to triggers like those shown in Fig.1.13 and Fig.1.14. The only differmove up the path from O to A, at which point the flux density reachence between this curve and that of Fig.1.4 is that the output voltes a maximum. If the magnetising force is now reduced to zero, the age is initially at its maximum level and remains there until VIN curve does not retrace its original path, but instead moves from A to exceeds the upper threshold voltage, VTU. B, where the material exhibits a non-zero, “residual’’ flux density. In The hysteresis inherent in the Schmitt trigger is its most powerorder to reduce the flux density to zero, the magnetising force must ful attribute and results in a high degree of noise immunity, an be decreased to a negative value at point C. essential feature for circuits like zero-crossing detectors working Any further negative excursions of H cause the curve to follow on noisy mains-derived signals. However, as we shall see later in the path from C to D, but if the magnetising force is now returned this series, the Schmitt trigger’s versatility lends it to many other to zero the curve follows path D to E where the material displays applications. OUTPUT VOLTAGE VOUT

OUTPUT VOLTAGE VOUT

VIN INCREASING

VOUT (HIGH)

VOUT (HIGH)

VIN INCREASING

VIN DECREASING

VIN DECREASING

VOUT (LOW)

VOUT (LOW)

HYSTERESIS VOLTAGE VH

HYSTERESIS VOLTAGE VH

INPUT VOLTAGE VIN

INPUT VOLTAGE VIN VTL

VTU

Fig.1.4. Input/Output relationship for the noninverting Schmitt trigger.

Everyday Practical Electronics, November 2000

VTL

VTU

Fig.1.5. Input/Output relationship for the inverting Schmitt trigger.

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has no effect on the switching function: VC2 changes state only once as VB1 crosses the upper threshold and does not change state again until VB1 has fallen low enough to cross the lower threshold. The introduction of positive feedback converts the simple comparator into a Schmitt trigger. This is an important concept which can be restated as follows. Negative feedback tends to keep an amplifier within its linear region; positive feedback tends to force it into saturation. The Schmitt trigger is a bistable device, i.e., it has two stable states and can remain in either state indefinitely until the input signal crosses a threshold and changes the state. In this respect, it behaves as a memory element, and with a little modification, the two-transistor version shown in Fig.1.1 can form a logic-level bistable device, similar to the type used as a single-bit memory element in early computer systems.

VB2 VH

VTU (UPPER THRESHOLD) VTL (LOWER THRESHOLD)

VB1 WITH SUPERIMPOSED NOISE

VCC

VC2 TIME

Fig.1.6. Adding hysteresis to a comparator eliminates the effect of noise.

Determining Thresholds

For the single-rail Schmitt trigger of Fig.1.1, the thresholds are defined by the following equations: Lower threshold voltage, R5 × ((R2 × VCC) + (R1 × VBE2)) (volts) (R1 × R5) + (R2 × (R1 + R4 + R5)) where VBE2 is the forward-biased base-emitter voltage of TR2. Upper threshold voltage, VTL =

VTU =

R5 × ((R2 × hFE2 × VCC) + ((R1 + R4) × VBE2)) (volts) (R2 × hFE2) × (R1 + R4 + R5) + (R5 × (R1 + R4))

Fortunately, these somewhat unwieldy expressions can be simplified. For example, if we make R1 = R2, the expression for VTL becomes: Lower threshold voltage, VTL =

R5 × (VCC + VBE2) R1 + R4 + (2 × R5)

(volts)

Also, if we assume that hFE2, the common-emitter current gain of TR2, is large (in the order of 100 or more), and if R2 and R5 are similar in magnitude, the expression for VTU reduces to: Upper threshold voltage, VTU =

R5 × VCC R1 + R4 + R5

(volts)

Clearly, the accuracy and stability of each threshold will depend on the tolerance and stability of the resistors used, and also on the supply voltage, VCC. For example, it is not uncommon for a “regulated’’ +5V supply to vary by as much as ±5% from its nominal value, and since each threshold is directly proportional to VCC they, too, will vary by this amount. Furthermore, VTL is also dependent on VBE2, which may vary considerably with factors such as base current, collector-emitter voltage, temperature, etc. To check the accuracy of the expressions for VTL and VTU, the circuit was built using 10k9 (ten kilohms) resistors for R1, R2, R3 and R4, and 20k9 for R5. Also, VCC was set to precisely 5·00V, and a value of 520mV was used for VBE2 (determined by in-circuit measurements). Transistor type BC108B was chosen for TR1 and TR2, although any other npn with an hFE of at least 100 would suffice. The simple equations yield values of VTL = 1·84V and VTU = 2·5V. To test the circuit, a 500Hz triangle wave input voltage, set to

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swing from 0·5V to 4·5V was used; the source resistance, RSOURCE, was zero. A triangle wave is the ideal input signal shape for testing Schmitt triggers: by observing the triangle at the base of transistor TR1 on a carefully zeroed oscilloscope trace and by overlapping the output waveform (in this case, VC2) using a second trace, the points at which the output signal’s transitions cut the triangle wave indicate the precise values of the thresholds. In this case, they measured VTL = 1·90V and VTU = 2·35V; reasonably close to the design values stated.

Speed and Frequency Response

So far, we’ve only considered the low-frequency response of the Schmitt trigger; the high-frequency response is limited primarily by the transistors, which take a finite time to turn on and off. These switching times are influenced by internal junction capacitances, which must be charged and discharged every time the device makes a transition from non-conducting to conducting, and back again. A thorough analysis of the switching behaviour of bipolar transistors is beyond the scope of this article; a good rule of thumb, however, is that the more current there is available to charge and discharge the internal capacitances, the faster the transistor can switch. Therefore, achieving good high-frequency response in all transistor circuits, whether discrete or integrated, tends to require the use of relatively low impedances (this is why the current consumption of high-frequency devices such as wideband op.amps is usually much greater than that of their low-frequency counterparts). To illustrate the effect of impedance levels on switching speed, two versions of the circuit of Fig.1.1 were built, each using BC108B transistors, but with different resistor values. For the first circuit, large values were selected: R1, R2, R3 and R4 = 100k9 and R5 = 200k9; for the second, using the same ratio of resistances, but a hundred times smaller: R1, R2, R3 and R4 = 1k9 and R5 = 2k9. An 80kHz triangle wave was fed to the input of each Schmitt trigger and the output waveform at the collector of TR2 was observed. The resulting waveforms shown in the oscillograph of Fig.1.7 illustrate the dramatic performance difference between the two circuits. The middle trace is the output waveform of the circuit using high resistances: clearly, the collector signal is grossly distorted. The bottom waveform, on the other hand, is the collector signal of the circuit using low resistances: note how the rectangular waveshape is well-formed and makes rapid transitions (less than 200ns) from one state to the other.

Fast Devices

At very high frequencies, general purpose transistors like the BC108B are often inadequate for fast switching, even when low resistances are used in the circuit. It then becomes necessary to use special transistors, specifically designed for fast-switching applications. To demonstrate the improvements in switching speed available from these fast devices, two further versions of the Schmitt trigger of Fig.1.1 were built. Each used the same low resistance values (R1, R2, R3 and R4 = 1k9 and R5 = 2k9), but one was built using BC108B transistors, the other using Zetex ZTX314 high-speed switching transistors. The response of each circuit to a 1MHz triangle wave input is shown in Fig.1.8. The middle trace shows the response of the BC108B circuit, where TR2’s collector waveform starts to rise about 40ns after VIN has crossed the 2·5V upper threshold. The performance of the ZTX314 circuit is shown in the lower trace, where the ZTX314 starts to turn off almost at the instant VIN crosses the upper threshold, and its collector voltage has reached its high level (VCC) some 40ns before the BC108B. The major difference, however, is in the transistors’ turn-on time. In the lower trace, the ZTX314 begins to turn on almost as soon as VIN has crossed the lower threshold, whereas the BC108B takes around 200ns before it begins to conduct sufficiently for the collector waveform to fall from VCC to its low level. Not only do these switching delays limit the maximum frequency response of the BC108B circuit, they also cause a shift in the effective threshold values. Looking again at the middle trace, TR2’s high to low transition occurs when VIN has reached a minimum, such that the effective lower threshold is zero. The ZTX314, on the other hand, makes the transition when VIN is very close to the nominal lower threshold value of 1·84V.

Everyday Practical Electronics, November 2000

Fig.1.7. Resistor values have a marked effect on highfrequency performance. Top trace: VIN (2V/div.). Middle trace: Output waveform using high resistance values (1V/div.). Bottom trace: Output waveform using low resistance values (1V/div.). Timebase: 2ms/div. There are, however, disadvantages to using high speed devices like the ZTX314. One is price: the ZTX314 tends to cost a few pence more than the BC108B. Also, the process of tailoring a transistor for high speed applications may require other parameters to be sacrificed: for example, the hFE of the BC108B is in the region 200 to 450; that of the ZTX314, on the other hand, is only 30 to 120.

Fig.1.8. Fast-switching transistors provide improved highfrequency performance. Top trace: VIN (2V/div.). Middle trace: Output waveform using BC108B devices (1V/div.). Bottom trace: Output waveform using ZTX314 devices (1V/div.). Timebase: 200ns/div. VOLTAGE SOURCE

CIRCUIT OR DEVICE

RSOURCE

VIN

VT

RIN

CIN

IB

Input Impedance

The inputs to most active devices like amplifiers, comparators, ADCs, and so on, can be modelled by the circuit of Fig.1.9, where RSOURCE represents the internal resistance (sometimes termed “output resistance’) of the voltage source, and VT represents the terminal voltage appearing at the output of the voltage source. (For the case of the Schmitt trigger in Fig.1.1, VT would equal VB1). RIN and CIN represent the resistance and capacitance seen “looking into’’ the input terminals of the circuit or device, and IB represents a bias current which may flow into or out of the circuit. For the circuit of Fig.1.1 operating at low frequencies, we are primarily concerned with IB1, the base current flowing into transistor TR1, although at higher frequencies the effects of CIN (TR1’s base capacitance plus any stray capacitances) must also be considered. The effect of IB1 is to cause a voltage drop across RSOURCE making the voltage at TR1’s base less than the input voltage VIN. This has the effect of increasing the apparent threshold voltages: although the actual thresholds measured at TR1’s base remain fixed, the voltage drop across RSOURCE means that VIN has to rise to a higher voltage in order for VB1 to cross the thresholds. For example, with resistors R1 to R4 = 1kW, R5 = 2kW, and using BC108Bs, it was found that increasing RSOURCE from zero to 100kW caused the apparent values of VTU and VTL to increase by 260mV and 700mV, respectively, relative to their nominal values. We’ll examine the effects of input impedance in more detail later in this series, when we look at Schmitt triggers based on op.amps, comparators and digital gates.

Four Better Than Two

The two-transistor Schmitt trigger circuit of Fig.1.1 is simple, inexpensive, and can be very effective in undemanding applications such as “squaring up’’ a sinewave or removing interference from a noisy signal. However, it does have two significant disadvantages. First, referring to the equations for VTU and VTL, we see that the thresholds are highly interdependent: changing any resistor value to vary one threshold will also vary the other. Therefore, selecting appropriate values to define specific thresholds can be extremely difficult. The second disadvantage is that the output signal at TR2’s collector has a limited output swing. Referring to the bottom trace of Fig.1.7, we see that the output signal amplitude is less than 2V;

Everyday Practical Electronics, November 2000

Fig.1.9. Simple model for input parameters of circuit or device. whilst this may be adequate for certain applications, it would hardly be sufficient to satisfy the logic levels of a digital gate operating on the same 5V supply. Both of these disadvantages can be eliminated by introducing two more transistors as shown in the circuit diagram Fig.1.10, where positive feedback is again applied to the base of TR2, but this time via TR3 and TR4. (Note transistor TR4 is a pnp type.) The circuit works as follows. Assume VB1 is zero such that transistor TR1 is off and provides no base current for TR4. Since TR4 is off, TR3 also receives no base drive and it, too, is off. Consequently, resistors R3, R4 and R5 form a potential divider which sets TR2’s base voltage (VB2) to a fraction of the supply voltage; if we assume TR1 and TR2 are matched, the value of VB2 equals the upper threshold voltage, VTU. If resistor R2 is similar in magnitude to R3, R4 and R5, and if TR2’s hFE is large, the upper threshold is given by: Upper threshold voltage, VTU =

(R4 + R5) × VCC R3 + R4 + R5

(volts)

When VB1 exceeds VTU, transistor TR1 begins to conduct and biases TR4 on, which in turn provides base drive for TR3. Provided resistors R6 and R7 are correctly sized, TR3 will be biased fully on and, if we assume its collector-emitter saturation voltage VCE3(sat) is zero, R5 is effectively shorted out. The effect is to “pull down’’ TR2’s base, which in turn reduces the emitter voltage VE causing TR1 to turn on even harder.

On Balance

Again, we have a regenerative action which causes TR1 and TR2 to change state rapidly. TR2’s lower base voltage now constitutes the lower threshold voltage: Lower threshold voltage, VTL =

R4 × VCC R3 + R4

(volts)

845

VCC (+5V)

TRANSISTOR CONNECTIONS (BOTTOM VIEW)

R1

TR4

c b e

e

BC546B BC556B

C1 100n

b

TR1 RSOURCE

VIN

TR2 c

c

e

e

b

c

R3

VOUT

b

VBE1

R6 R4

VBE2

TR3 c

VB2

VB1

b

VE e R2

R5

Actual Performance

R7 0V

Fig.1.10. A four-transistor Schmitt trigger offers improved performance. Note: Here transistors TR1 to TR3 are BC546s and TR4 is a BC556. Note that this equation does not contain R5, thus allowing VTU to be set independently of VTL. For given values of VCC and VTL, R3 and R4 can be found from: R3 =

R4 × (VCC – VTL) VTL

(ohms)

Knowing VTU, it is then a simple matter to calculate R5: R5 =

VTU × (R3 + R4) – (VCC × R4) VCC – VTU

(ohms)

In practice, the thresholds are affected slightly by the values of resistors R1 and R2, and, to some extent, by R6 and R7. For fast response, R6 and R7 must be fairly small (a few kilohms) to ensure transistor TR3 can be turned on and off quickly. However, the resulting current required from TR4’s collector places demands on TR1’s collector current which must supply TR4’s base drive. Consequently, resistor R1 should be fairly large such that all of TR1’s collector current is available to TR4’s base; however, for fast response, R1 should be small enough to “suck’’ stored charge out of TR4’s base region, such that it turns off quickly. The current available to TR4’s base also depends on resistor R2, which sets an upper limit on TR1’s collector current. For a given VTU, making R2 small will maximise TR1’s collector current; however, if R2 is too small, the increased base current taken by TR2 (when VB1 is below VTU) tends to “load’’ the R3-R4-R5 network, causing VTU to be lower than the value predicted by the equation above. All these conflicting requirements demand a careful balance of resistor values for proper operation. Generally, if all the resistors are of similar magnitude, and if VTU and VTL are set within the range 1·25V to 4V (assuming VCC = 5V), the actual thresholds will be fairly close to their nominal values. Note that the output is taken from transistor TR4’s collector rather than TR2 (TR2’s collector resistor is no longer required). When the input voltage rises above VTU, the voltage output VOUT rises to VCC as TR4 turns on; when VIN falls below VTL, the output is pulled down toward 0V by resistors R6 and R7. Thus, like the simple two-transistor Schmitt trigger, the output is “in phase’’ with the input, but with a much greater swing, typically 0 to 5V when the output is lightly loaded.

Input Signal Range

Transistor TR1’s base voltage should not be allowed to go too far negative, otherwise its base-emitter junction could break down. Devices like the BC108B and BC546B have a maximum reverse-biased base-emitter voltage of around 5V; if this is exceeded, the junction can “avalanche’’ and conduct excessive current. Thus, if VTL is set to, say, 2·5V such that the emitter potential is around 2V, VB1 should not be permitted to go more negative than –3V. So far, we’ve been working with a supply voltage of 5V, but there’s no reason why this should not be increased, provided the resistors are rated accordingly and the maximum collector-emitter voltage, VCEO(max), of the transistors is not exceeded. For transistors

846

like the BC546 and BC556 (see below), VCEO(max) is around 60V; however, for the BC108 it is only 25V, and for devices like the ZTX314 it can be as low as 15V, so it is necessary to limit VCC accordingly. When VB1 exceeds VTU and transistor TR1 turns on, its collector voltage is effectively clamped at one diode-drop below VCC by TR4’s base-emitter junction. However, as TR1’s base voltage rises so, too, does its emitter voltage. Eventually, when VB1 is roughly equal to VCC, TR1 saturates, and any further increase in VB1 causes the voltage across resistor R1 to decrease below the diode-drop needed to bias TR4 on. The result is that TR4 switches off, and VOUT makes a sudden transition from VCC to 0V. Thus, for correct operation, input VIN should not be permitted to rise to within, say, half a volt of VCC. To check the circuit performance of Fig.1.10, BC546B npn transistors were used for TR1 to TR3, and a BC556B pnp for TR4 (these are general purpose, medium-gain devices). With VCC = 5·00V and R6 = 3·3k9 and R7 = 1·5k9, values of 1k9 for R1, R2; 2k9 for R3; 5109 for R4 and 7·5k9 for R5 were chosen to provide nominal thresholds of VTL = 1·02V and VTU = 4·00V. By inputting a 150Hz triangle wave (RSOURCE = 0), the actual thresholds were measured as VTL = 1·30V and VTU = 3·98V. Although the upper threshold was almost “spot on’, VTL was about 0·3V higher than its design value. Why? When transistor TR1 is on, its collector current is roughly equal to its emitter current. Therefore, since the value of R1 is the same as R2 in this example, the voltage across each resistor will be the same. To keep transistor TR4 fully on, we need at least 0·65V across R1 – and, hence, across R2 – to provide sufficient voltage to forward bias TR4’s base-emitter junction. Now, the voltage across R2, VE = VB1 – VBE1, so if we take VBE1 = 0·65V, it follows that VE will drop below 0·65V when VB1 falls below 1·3V. Thus, TR4 starts to turn off when input VIN falls to 1·3V, resulting in VTL being 300mV higher than its design value. The simple solution to this problem is to increase the value of R1 to make more voltage available to TR4’s base when VE is low. With R1 increased to 10k9, VTL measured 1·02V – exactly equal to the design value!

Want More Speed? Get Clamped!

Like the two-transistor Schmitt, the resistance values of the fourtransistor version should be kept low for good high-frequency response. However, this alone is sometimes not enough. When a bipolar transistor saturates (i.e., when VCE ≈ 0), an excess of minority charge carriers gets stored in the base region. Therefore, to ensure the transistor can turn off quickly requires either that it is not allowed to saturate, or that the stored charge must be removed rapidly from the base. For the Schmitt trigger, failure to ensure rapid transistor turn off can cause significant errors in the apparent threshold values at high frequencies. For example, values of 1k9 for R1, R2, R4 and R5, and 2k9 for R3 were chosen to give nominal threshold values of VTL = 1·67V, VTU = 2·5V at VCC = 5·00V. With resistor R6 set to 2·2k9 and 22k9 selected for R7, the actual low-frequency thresholds (measured at 150Hz) were 1·72V (VTL) and 2·48V (VTU), and the corresponding voltage levels at TR2’s base were 1·70V and 2.48V. So far, so good. However, with the input frequency increased to 150kHz, the thresholds had merged into one, and TR2’s base voltage was a constant 1·70V, even though TR4 was switching on and off. Closer inspection revealed that transistor TR3 had turned on, but could not turn off because resistor R7 was too large to provide the low-resistance path necessary to remove the charge stored in its base region. Reducing the value of resistor R7 to 470 ohms corrected the problem, allowing TR3 to turn off properly: TR2’s base voltages were now 1·70V and 2·50V, roughly the same as the low-frequency values. However, the actual thresholds were now 1·24V (VTL) and 2·58V (VTU). Clearly, TR1 and TR4 were switching on quickly, such that VTU was roughly the same as its low-frequency value; however, TR4 was switching off relatively slowly, resulting in the effective value of VTL being significantly less than its low-frequency value (1·72V). Reducing R1 to 680 ohms helped to turn off TR4 more quickly by removing more of the stored charge from its saturated base. However, this measure only succeeded in raising VTL to 1·37V, still some 300mV short of its design value.

Everyday Practical Electronics, November 2000

Although changing transistor TR4 to a faster device would certainly help, an alternative solution is to prevent TR4 from saturating. This is achieved by adding two diodes, D1 and D2, as shown in the circuit diagram Fig.1.11. This arrangement, known as a “Baker Clamp’’, works as follows. When transistor TR1 turns on, its collector is clamped at two diode drops below VCC (there is one diode drop across TR4’s baseemitter junction, and another across D1). Transistor TR4 now turns on and its collector rises toward VCC, VCC (+5V) forward biasing C1 R1 TR4 100n diode D2. e b Since D2 is the 0V a same diode type as D1 D2 c VOUT k IN4148 IN4148 D1, it will exhibit a TR1 similar voltage a k c drop, such that its b R6 anode (a) will rise e to the same potential as D1’s anode. The result is that TR4’s collector can- Fig.1.11. The addition of a “Baker not rise any higher Clamp’’ improves switching speed. than its base, such that its collector-emitter voltage will be the same as its baseemitter voltage, preventing it from saturating. The waveforms shown in Fig.1.12 illustrate the performance of the Baker Clamp, where the upper trace is the input triangle wave at 150kHz. The bottom trace shows the output response without diodes D1 and D2; the middle trace shows VOUT with D1 and D2 fitted as shown in Fig.1.11. Notice how the clamp makes TR4 turn off some 460ns more quickly than it does without the clamp. As a result, the high-frequency response was much improved: with the clamp in place, VTL was 1·64V, almost equal to its ideal, design value (1·67V). Also, notice that the amplitude of the middle trace is only about 4·4V; the presence of the clamp means that VOUT can only swing from 0V to one diode drop below VCC.

Fig.1.12. Waveforms showing Baker Clamp improvements. Top trace: VIN (5V/div.). Middle trace: Output waveform with Baker Clamp fitted (2V/div.). Bottom trace: Output waveform without Baker Clamp (2V/div.). Timebase: 1ms/div.

VCC (+5V) R1 VOUT

C1 100n

RSOURCE

TR1

RIN

VIN

e

VB1

TR2

(volts)

When transistors TR1 and TR2 turn on, TR1’s collector voltage falls to a lower value, thereby “pulling down’’ TR2’s base; again, we see positive feedback causing a regenerative action which causes both devices to turn on harder. Assuming TR2’s base current is negligibly small, its base voltage is now: (volts) TR2 base voltage,VB2 = (VCE1 + VBE2) × R3 R2 Transistor TR1 will turn off when VB1 falls below VBE1 + VBE2 + VB2; therefore, assuming TR1 is saturated when “on’’, such that VCE1 (= VCE1(sat)) is much less than VBE2, the lower threshold relative to TR1’s base is: Lower threshold voltage,

R3 0V

Fig.1.13. Circuit diagram for a Schmitt trigger using complementary transistors. which change with temperature and exhibit part-to-part variations. Also, VOUT does not swing from 0V to VCC, but covers only a fraction of this range and is influenced considerably by the values selected for the thresholds. A sufficiently large input resistance, RIN, is required, otherwise, when TR1 turns on, its collector voltage gets “pulled up’’ as VIN rises, thereby distorting the output signal (although RIN may be omitted if RSOURCE is large enough).

Variation on a Theme

A variation on the complementary theme is shown in the circuit diagram Fig.1.14. When VIN is low, TR1 and TR2 are both off, and resistors R2 and R3 set TR1’s base voltage to VB1 = VCC × R3/(R2+R3). As VIN rises and the voltage at TR1’s emitter reaches VB1+VBE1, TR1 starts to conduct. If both devices have large hFE, we can ignore their base currents and assume that all of TR1’s emitter current flows through resistor R1 to 0V. The voltage on R1 increases until it equals VBE2, TR2’s base-emitter forward-bias voltage. Transistor TR2 now starts to conduct and provides more base current for TR1, which in turn provides more base drive for TR2 and the familiar regenerative process continues until both devices are fully on. TR1’s base voltage, which is also the output voltage VOUT(1), falls from its initial value given above, to a very low value defined by TR2’s saturation voltage, VCE2(sat). The upper threshold voltage relative to VIN is given by: Upper threshold voltage, VTU = VB1 + VBE1 + (RSOURCE + RIN) × VBE2 R1

(volts)

Notice that this circuit is an “inverting’’ Schmitt trigger, in that the output voltage at TR1’s collector falls when VIN rises above VTU. Although relatively simple, the circuit has several drawbacks; in particular, the thresholds are highly dependent on VBE1 and VBE2,

Everyday Practical Electronics, November 2000

b

VB2

In order to forward bias TR1 and TR2, VB1 must rise to VBE1 + VBE2 + VB2, so the upper threshold voltage relative to TR1’s base is: Upper threshold voltage, (volts) VTU = VBE1 + VBE2 + (R3 × VCC) R1 + R2 + R3

VTL = VBE1 + VBE2 × (1 + R3/R2)

VBE2

c

The differential pair common to both the two- and four-transistor Schmitt triggers is a powerful topology used extensively in many circuits, both discrete and integrated. However, before concluding our look at discrete circuits, it’s worth considering two Schmitt triggers that use a complementary arrangement. In the circuit diagram of Fig.1.13, complementary transistors TR1 and TR2 are both cut off when input VIN, and hence VB1, is zero. Under these conditions, TR2’s base voltage is set by VCC and the potential divider R1–R2–R3: R3 × VCC R1 + R2 + R3

R2

e

VBE1

Complementary Schmitt

TR2 base voltage, VB2 =

c

b

(volts)

and so: VTU = VCC × R3 + VBE1 + (RSOURCE + RIN) × VBE2 (R2 + R3) R1

(volts)

847

As VIN falls, TR1 and TR2 will start to turn off when TR1’s emitter voltage, VE1 falls below VBE2 + VCE1(sat) (assuming TR1 is saturated when conducting). However, VE1 = VIN – IE1 × (RSOURCE + RIN), and since IE1 ≈ IC1 = VBE2/R1, the transistors will start to turn off when: VIN – (RSOURCE + RIN) × VBE2 = VBE2 + VCE1(sat) R1 Rearranging and putting VIN = VTL gives: Lower threshold voltage, VTL = VCE1(sat) + VBE2 × (1 + (RIN + RSOURCE)/R1)

(volts)

(volts)

can be omitted if RSOURCE is large enough. Again, the thresholds are highly dependent on transistor parameters like VBE and VCE(sat). Output voltage VOUT(1) swings from near zero to a high level defined by resistors R2 and R3; this limited range can be improved by adding resistor R4, transistor TR3 and RL (RL can be a simple pullup resistor, or could be a load such as a relay or l.e.d.). The additional stage provides a second output voltage, VOUT(2), with a range of approximately zero to VCC. Note, however, that R4 and TR3 must be considered in parallel with R3 when determining the threshold values; also, VOUT(2) is inverted with respect to VOUT(1).

Looking Ahead

For non-demanding applications, the discrete Schmitt triggers we’ve examined can sometimes provide a simple, cheap solution. Like the previous circuit, RIN (required to limit the input current) However, achieving a degree of precision demands careful attention to factors such as transistor matching, resistor values and biasing levels, particularly for highVCC (+5V) frequency applications. Life would be much RIN RSOURCE RL R2 IE1 simpler if we could combine the differential VBE1 pair with some extra gain stages and a wideVOUT(1) VOUT(2) TR1 e range output stage and enclose the whole lot TR3 c inside a “black box’. b R4 VIN TR2 c b Fortunately, devices like the operational c IC1 C1 b amplifier (op.amp) and the comparator do VE1 e 100n VB1 just that. Next month, we shall see in Part e R3 Two how the op.amp frees us from most of VBE2 R1 the design work associated with discrete cir0V cuits, and instead allows us to focus on the Schmitt trigger as an interesting and versatile circuit “element’’. Fig.1.14. Alternative complementary-transistor Schmitt trigger circuit.

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H.P. 6012B DC PSU, 0-60V, 0-50A, 1000W . . . . . . . . . . . . .£1000 FARNELL AP60/50 1kW Autoranging . . . . . . . . . . . . . . . . .£1000 FARNELL H60/50 0-60V, 0-50A . . . . . . . . . . . . . . . . . . . . . .£750 FARNELL H60/25 0-60V, 0-25A . . . . . . . . . . . . . . . . . . . . . .£400 Power Supply HPS3010 0-30V, 0-10A . . . . . . . . . . . . . . . . .£140 FARNELL L30-2 0-30V, 0-2A . . . . . . . . . . . . . . . . . . . . . . . . .£80 FARNELL L30-1 0-30V, 0-1A . . . . . . . . . . . . . . . . . . . . . . . . .£60 Many other Power Supplies available Isolating Transformer 250V In/Out 500VA . . . . . . . . . . . . . . .£40

SPECTRUM ANALYSERS TEKTRONIX 492 50kHz-18GHz . . . . . . . . . . . . . . . . . . . . .£3500 EATON/AILTECH 757 0·001-22GHz . . . . . . . . . . . . . . . . . .£2500 ADVANTEST R3261A 9kHz-2·6GHz, synthesised . . . . . . .£4000 H.P. 853A (Dig. Frame) with 8559A 100kHz-21GHz . . . . . .£2750 H.P. 8558B with main frame, 100kHz-1500MHz . . . . . . . . .£1250 H.P. 3580A Audio Analyser 5Hz-50kHz, as new . . . . . . . . .£1000 MARCONI 2382 100Hz-400MHz, high resolution . . . . . . . .£2000 B&K 2033R Signal Analyser . . . . . . . . . . . . . . . . . . . . . . . .£1500 ADVANTEST TR4131 10kHz-3·5GHz . . . . . . . . . . . . . . . . .£2750 MARCONI 2370 30Hz-110MHz . . . . . . . . . . . . . . . . . .from £500 H.P. 141 SYSTEMS 8553 1kHz-110MHz . . . . . . . . . . . . . . . . . . . . . . . . . . .from £500 8554 500kHz-1250MHz . . . . . . . . . . . . . . . . . . . . . . . .from £750 8555 10MHz-18GHz . . . . . . . . . . . . . . . . . . . . . . . . . .from £1000 UNUSED OSCILLOSCOPES TEKTRONIX TDS640A 4-ch., 500MHz, 2G/S . . . . . . . . . . .£4000 TEKTRONIX TDS380 dual trace, 400MHz, 2G/S. . . . . . . . .£2000 TEKTRONIX TDS350 dual trace, 200MHz, 1G/S . . . . . . . .£1250 TEKTRONIX TAS485, 4-ch., 200MHz, etc. . . . . . . . . . . . . . .£900 H.P. 54600B dual trace, 100MHz, 20M/S . . . . . . . . . . . . . . .£900 OSCILLOSCOPES PHILIPS PM3092 2+2-ch., 200MHz, delay, etc., £800 as new£950 PHILIPS PM3082 2+2-ch., 100MHz, delay etc., £700 as new £800 TEKTRONIX TAS465 dual trace, 100MHz, delay etc. . . . . . .£800 TEKTRONIX 2465B 4-ch., 400MHz, delay cursors etc . . . .£1250 TEKTRONIX 2465 4-ch., 300MHz, delay cursors etc. . . . . . .£900 TEKTRONIX 2445/A/B 4-ch 150MHz, delay cursors etc .£500-£900 TEKTRONIX 468 dig. storage, dual trace, 100MHz, delay . . . .£450 TEKTRONIX 466 Analogue storage, dual trace, 100MHz . . . .£250 TEKTRONIX 485 dual trace, 350MHz, delay sweep . . . . . . .£600 TEKTRONIX 475 dual trace, 200MHz, delay sweep . . . . . . .£400 TEKTRONIX 465B dual trace, 100MHz, delay sweep . . . . . .£325 PHILIPS PM3217 dual trace, 50MHz delay . . . . . . . . .£250-£300 GOULD OS1100 dual trace, 30MHz delay . . . . . . . . . . . . . .£200 JUST IN HAMEG HM303.4 dual trace, 30MHz component testerrr . . .£325 HAMEG HM303 dual trace, 30MHz component tester . . . . . .£300 HAMEG HM203.7 dual trace, 20MHz component tester . . . .£250 FARNELL DTV20 dual trace, 20MHz component tester . . . .£180

GOULD OS 300

WELLER EC3100A Temperature controlled Soldering Station 200°C-450°C. Unused

£125

£160

Dual Trace, 20MHz MANY OTHER OSCILLOSCOPES AVAILABLE

Used Equipment – GUARANTEED. Manuals supplied This is a VERY SMALL SAMPLE OF STOCK. SAE or Telephone for lists. Please check availability before ordering. CARRIAGE all units £16. VAT to be added to Total of Goods and Carriage

Everyday Practical Electronics, November 2000

WHETHER ELECTRONICS IS YOUR HOBBY OR YOUR LIVELIHOOD . . . YOU NEED THE MODERN ELECTRONICS MANUAL and the ELECTRONICS SERVICE MANUAL

THE MODERN ELECTRONICS MANUAL

E SAL

40%F OF

The essential reference work for everyone studying electronics

% off at 40 l a u ore. r Man ce. eithe gular pri e even m Buy v re a s h and y bot u b ISS r O

M N’T IS! O D TH

) Over 900 pages ) In-depth theory ) Projects to build ) Detailed assembly instructions ) Full components checklists ) Extensive data tables ) Detailed supply information ) Easy-to-use format ) Clear and simple layout ) Comprehensive subject range ) Professionally written ) Regular Supplements ) Sturdy gold blocked ring-binder

EVERYTHING YOU NEED TO GET STARTED AND GO FURTHER IN ELECTRONICS! The revised edition of the Modern Electronics Base Manual contains practical, easy-to-follow information on the following subjects: BASIC PRINCIPLES: Electronic Components and their Characteristics (16 sections from Resistors and Potentiometers to Crystals, Crystal Modules and Resonators), Circuits Using Passive Components (9 sections), Power Supplies, The Amateur Electronics Workshop, The Uses of Semiconductors, Digital Electronics (6 sections), Operational Amplifiers, Introduction to Physics, Semiconductors (6 sections) and Digital Instruments (5 sections). CIRCUITS TO BUILD: There's nothing to beat the satisfaction of creating your own project. From basic principles, like soldering and making printed circuit boards, to circuit-building, the Modern Electronics Manual and its Supplements describe clearly, with appropriate diagrams, how to assemble radios, loudspeakers,

amplifiers, car projects, computer interfaces, measuring instruments, workshop equipment, security systems, etc. The Base Manual describes 13 projects including a Theremin and a Simple TENS Unit. ESSENTIAL DATA: Extensive tables on diodes, transistors, thyristors and triacs, digital and linear i.c.s. EXTENSIVE GLOSSARY: Should you come across a technical word, phrase or abbreviation you're not familiar with, simply turn to the glossary included in the Manual and you'll find a comprehensive definition in plain English. The Manual also covers Safety and Suppliers. The most comprehensive reference work ever produced at a price you can afford, the revised edition of THE MODERN ELECTRONICS MANUAL provides you with all the essential information you need.

THE MODERN ELECTRONICS MANUAL Revised Edition of Basic Work: Contains over 900 pages of information. Edited by John Becker. Regular Supplements: Approximately 160-page Supplements of additional information which, if requested, are forwarded to you immediately on publication (four times a year). These are billed separately and can be discontinued at any time. Presentation: Durable looseleaf system in large A4 format

Price of the Basic Work: £39.95 SALE PRICE £23.97 (to include a recent Supplement FREE)

Guarantee Our 30 day money back guarantee gives you complete peace of mind. If you are not entirely happy with either Manual, for whatever reason, simply return it to us in good condition within 30 days and we will make a full refund of your payment – no small print and no questions asked. (Overseas buyers do have to pay the overseas postage charge)

Wimborne Publishing Ltd., Dept Y11, Allen House, East Borough, Wimborne, Dorset BH21 1PF. Tel: 01202 881749. Fax: 01202 841692.

ELECTRONICS SERVICE MANUAL EVERYTHING YOU NEED TO KNOW TO GET STARTED IN REPAIRING AND SERVICING ELECTRONIC EQUIPMENT SAFETY: Be knowledgeable about Safety Regulations, Electrical Safety and First Aid. UNDERPINNING KNOWLEDGE: Specific sections enable you to Understand Electrical and Electronic Principles, Active and Passive Components, Circuit Diagrams, Circuit Measurements, Radio, Computers, Valves and manufacturers' Data, etc. PRACTICAL SKILLS: Learn how to identify Electronic Components, Avoid Static Hazards, Carry Out Soldering and Wiring, Remove and Replace Components. TEST EQUIPMENT: How to Choose and Use Test Equipment, Assemble a Toolkit, Set Up a Workshop, and Get the Most from Your Multimeter and Oscilloscope, etc. SERVICING TECHNIQUES: The regular Supplements include vital guidelines on how to Service Audio Amplifiers, Radio Receivers, TV Receivers, Cassette Recorders, VIdeo Recorders, Personal Computers, etc. TECHNICAL NOTES: Commencing with the IBM PC, this section and the regular Supplements deal with a very wide range of specific types of equipment – radios, TVs, cassette recorders, amplifiers, video recorders etc.. REFERENCE DATA: Detailing vital parameters for Diodes, Small-Signal Transistors, Power Transistors, Thyristors, Triacs and Field Effect Transistors. Supplements include Operational Amplifiers, Logic Circuits, Optoelectronic Devices, etc.

The essential work for servicing and repairing electronic equipment )Around 900 pages )Fundamental principles )Troubleshooting techniques )Servicing techniques )Choosing and using test equipment )Reference data )Easy-to-use format )Clear and simple layout )Vital safety precautions )Professionally written )Regular Supplements )Sturdy gold blocked ring-binder

ELECTRONICS SERVICE MANUAL Basic Work: Contains around 900 pages of information. Edited by Mike Tooley BA Regular Supplements: Approximately 160-page Supplements of additional information which, if requested, are forwarded to you immediately on publication (four times a year). These are billed separately and can be discontinued at any time. Presentation: Durable looseleaf system in large A4 format

Price of the Basic Work: £39.95 SALE PRICE £23.97 (to include a recent Supplement FREE)

ORDER BOTH MANUALS TOGETHER AND SAVE ANOTHER £8 A mass of well-organised and clearly explained information is brought to you by expert editorial teams whose combined experience ensures the widest coverage Regular Supplements to these unique publications, each around 160 pages, keep you abreast of the latest technology and techniques if required REGULAR SUPPLEMENTS Unlike a book or encyclopedia, these Manuals are living works – continuously extended with new material. If requested, Supplements are sent to you approximately every three months. Each Supplement contains around 160 pages – all for only £23.50+£2.50 p&p. You can, of course, return any Supplement (within ten days) which

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Everyday Practical Electronics are pleased to be able to offer all readers these

ELECTRONICS CD-ROMS NEW

ELECTRONICS PROJECTS

Logic Probe testing

Audio Mixer circuit description

ANALOGUE ELECTRONICS

Complimentary output stage

Twin-T phase shifting network

Electronic Projects is split into two main sections: Building Electronic Projects contains comprehensive information about the components, tools and techniques used in developing projects from initial concept through to final circuit board production. Extensive use is made of video presentations showing soldering and construction techniques. The second section contains a set of ten projects for students to build, ranging from simple sensor circuits through to power amplifiers. A shareware version of Matrix’s CADPACK schematic capture, circuit simulation and p.c.b. design software is included. The projects on the CD-ROM are: Logic Probe; Light, Heat and Moisture Sensor; NE555 Timer; Egg Timer; Dice Machine; Bike Alarm; Stereo Mixer; Power Amplifier; Sound Activated Switch; Reaction Tester. Full parts lists, schematics and p.c.b. layouts are included on the CD-ROM.

Analogue Electronics is a complete learning resource for this most difficult branch of electronics. The CD-ROM includes a host of virtual laboratories, animations, diagrams, photographs and text as well as a SPICE electronic circuit simulator with over 50 pre-designed circuits. Sections on the CD-ROM include: Fundamentals – Analogue Signals (5 sections),Transistors (4 sections), Waveshaping Circuits (6 sections). Op.Amps – 17 sections covering everything from Symbols and Signal Connections to Differentiators. Amplifiers – Single Stage Amplifiers (8 sections), Multi-stage Amplifiers (3 sections). Filters – Passive Filters (10 sections), Phase Shifting Networks (4 sections), Active Filters (6 sections). Oscillators – 6 sections from Positive Feedback to Crystal Oscillators. Systems – 12 sections from Audio Pre-Amplifiers to 8-Bit ADC plus a gallery showing representative p.c.b. photos.

DIGITAL ELECTRONICS Digital Electronics builds on the knowledge of logic gates covered in Electronic Circuits & Components (opposite), and takes users through the subject of digital electronics up to the operation and architecture of microprocessors. The virtual laboratories allow users to operate many circuits on screen. Covers binary and hexadecimal numbering systems, ASCII, basic logic gates and their operation, monostable action and circuits, and bistables – including JK and D-type flip-flops. Multiple gate circuits, equivalent logic functions and specialised logic functions. Introduces sequential logic including clocks and clock circuitry, counters, binary coded decimal and shift registers. A/D and D/A converters and their parameters, traffic light controllers, memories and microprocessors – architecture, bus systems and their arithmetic logic units. Virtual laboratory – Traffic Lights

Microprocessor

FILTERS

Filter Theory

Active filter synthesis

DIGITAL WORKS 3.0

Macro screen

Counter project

PRICES Prices for each of the CD-ROMs above are:

Filters is a complete course in designing active and passive filters that makes use of highly interactive virtual laboratories and simulations to explain how filters are designed. It is split into five chapters: Revision which provides underpinning knowledge required for those who need to design filters. Filter Basics which is a course in terminology and filter characterization, important classes of filter, filter order, filter impedance and impedance matching, and effects of different filter types. Advanced Theory which covers the use of filter tables, mathematics behind filter design, and an explanation of the design of active filters. Passive Filter Design which includes an expert system and filter synthesis tool for the design of lowpass, high-pass, band-pass, and band-stop Bessel, Butterworth and Chebyshev ladder filters. Active Filter Design which includes an expert system and filter synthesis tool for the design of low-pass, high-pass, bandpass, and band-stop Bessel, Butterworth and Chebyshev op.amp filters.

Digital Works Version 3.0 is a graphical design tool that enables you to construct digital logic circuits and analyze their behaviour. It is so simple to use that it will take you less than 10 minutes to make your first digital design. It is so powerful that you will never outgrow its capability. )Software for simulating digital logic circuits )Create your own macros – highly scalable )Create your own circuits, components, and i.c.s )Easy-to-use digital interface )Animation brings circuits to life )Vast library of logic macros and 74 series i.c.s with data sheets )Powerful tool for designing and learning

Hobbyist/Student ...................................................£45 inc VAT Institutional (Schools/HE/FE/Industry)..............£99 plus VAT Institutional 10 user (Network Licence) ..........£199 plus VAT

(UK and EU customers add VAT at 17.5% to “plus VAT’’ prices)

Interested in programming PIC microcontrollers? Learn with PICtutor by John Becker This highly acclaimed CD-ROM, together with the PICtutor experimental and development board, will teach you how to use PIC microcontrollers with special emphasis on the PIC16x84 devices. The board will also act as a development test bed and programmer for future projects as your programming skills develop. This interactive presentation uses the specially developed Virtual PIC Simulator to show exactly what is happening as you run, or step through, a program. In this way the CD provides the easiest and best ever introduction to the subject. Nearly 40 Tutorials cover virtually every aspect of PIC programming in an easy to follow logical sequence. HARDWARE Whilst the CD-ROM can be used on its own, the physical demonstration provided by the PICtutor Development Kit, plus the ability to program and test your own PIC16x84s, really reinforces the lessons learned. The hardware will also be an invaluable development and programming tool for future work. Two levels of PICtutor hardware are available – Standard and Deluxe. The Standard unit comes with a battery holder, a reduced number of switches and no displays. This version will allow users to complete 25 of the 39 Tutorials. The Deluxe Development Kit is supplied with a plug-top power supply (the Export Version has a battery holder), all switches for both PIC ports plus l.c.d. and 4-digit 7-segment l.e.d. displays. It allows users to program and control all functions and both ports of the PIC. All hardware is supplied fully built and tested and includes a PIC16F84.

The Virtual PIC

PICtutor CD-ROM

HARDWARE

Hobbyist/Student . . . . . . . . . . . . . . . . . . . .£45 inc. VAT Institutional (Schools/HE/FE Industry) . . .£99 plus VAT Institutional 10 user (Network Licence) .£199 plus VAT

Standard PICtutor Development Kit . . . . . . .£47 inc. VAT Deluxe PICtutor Development Kit . . . . . . . .£99 plus VAT Deluxe Export Version . . . . . . . . . . . . . . . . .£96 plus VAT

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Deluxe PICtutor Hardware

ELECTRONIC COMPONENTS PHOTOS A high quality selection of over 200 JPG images of electronic components. This selection of high resolution photos can be used to enhance projects and presentations or to help with training and educational material. They are royalty free for use in commercial or personal printed projects, and can also be used royalty free in books, catalogues, magazine articles as well as worldwide web pages (subject to restrictions – see licence for full details). Also contains a FREE 30-day evaluation of Paint Shop Pro 6 – Paint Shop Pro image editing tips and on-line help included! Price

£19.95 inc. VAT

ELECTRONIC CIRCUITS & COMPONENTS + THE PARTS GALLERY

MODULAR CIRCUIT DESIGN This CD-ROM contains a range of tried and tested analogue and digital circuit modules, together with the knowledge to use and interface them. Thus allowing anyone with a basic understanding of circuit symbols to design and build their own projects. Essential information for anyone undertaking GCSE or “A’’ level electronics or technology and for hobbyists who want to get to grips with project design. Over seventy different Input, Processor and Output modules are illustrated and fully described, together with detailed information on construction, fault finding and components, including circuit symbols, pinouts, power supplies, decoupling etc.

Provides an introduction to the principles and application of the most common types of electronic components and shows how they are used to form complete circuits. The virtual laboratories, worked examples and pre-designed circuits allow students to learn, experiment and check their understanding. Sections include: Fundamentals: units & multiples, electricity, electric circuits, alternating circuits. Passive Components: resistors, capacitors, inductors, transformers. Semiconductors: diodes, transistors, op.amps, logic gates. Passive Circuits . Active Circuits The Parts Gallery will help students to recognise common electronic components and their corresponding symbols in circuit diagrams. Selections include: Components, Components Quiz, Symbols, Symbols Quiz, Circuit Technology

Single User Version £19.95 inc. VAT Multiple User Version £34 plus VAT

Hobbyist/Student...............................................................................£34 inc VAT Institutional (Schools/HE/FE/Industry)............................................£89 plus VAT Institutional 10 user (Network Licence)..........................................£169 plus VAT

(UK and EU customers add VAT at 17.5% to “plus VAT’’ prices)

(UK and EU customers add VAT at 17.5% to “plus VAT’’ prices) Minimum system requirements for these CD-ROMs: PC with 486/166MHz, VGA+256 colours, CD-ROM drive, 32MB RAM, 10MB hard disk space. Windows 95/98, mouse, sound card, web browser.

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Electronic Projects Analogue Electronics Version required: Digital Electronics Hobbyist/Student Filters Institutional Digital Works 3.0 Institutional 10 user PICtutor Electronic Circuits & Components +The Parts Gallery PICtutor Development Kit – Standard PICtutor Development Kit – Deluxe

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Electronic Components Photos Note: The software on each version is Modular Circuit Design – Single User the same, only the licence for use varies. Modular Circuit Design – Multiple User Full name: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Address: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .............................................................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . .Post code: . . . . . . . . . . . . . . . .Tel. No: . . . . . . . . . . . . . . . . . . . . Signature: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I enclose cheque/PO in £ sterling payable to WIMBORNE PUBLISHING LTD for £ . . . Please charge my Visa/Mastercard: £ . . . . . . . . . . . . . .Card expiry date: . . . . . . . . . Card No: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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ee50b

The small printed circuit board is available from the EPE PCB Service, code 270 (see page 868). Finally, please don’t forget to uprate the mains carrying cables if you intend switching high current appliances.

Sample-and-Hold PIC Pulsometer The 40MHz crystal timing module used in the PIC Pulsometer project is a 4-pin device which plugs directly into an 8-pin d.i.l. socket. It is an RS type and was ordered through Electromail (2 01536 304555 or http://rswww.com), their mail order outlet. They advertise two devices, codes 268-032 and 249-3779, and either will be OK in this circuit. Regarding the 16-character 1-line, back-lit, l.c.d. module, this was obtained from Maplin (2 0870 264 6000 or www.maplin.co.uk), code NT55K. They also supplied the ABS, sloping front case, code LH63T. For those readers unable to program their own PICs, a ready-programmed PIC16F84 can be purchased from Magenta Electronics (2 01283 565435 or www.magenta2000.co.uk) for the inclusive price of £5.90 (overseas readers add £1 for p&p). For those who wish to program their own PICs, the software is available from the Editorial offices on a 3·5in. PC-compatible disk, see PCB Service page 868. It is also available free via the EPE website: ftp://ftp.epemag.wimborne.co.uk/pub/PICS/ pulsometer.

Handclap Switch One or two components may cause buying problems when shopping for parts for the Handclap Switch project. Fortunately, they appear to be fairly standard items and our component advertisers should be able to offer devices with almost identical characteristics. The choice of a 12V relay will obviously depend on the appliance being “controlled’’ and the relay contacts must be rated accordingly. The one in the prototype was ordered from Rapid Electronics (2 01206 751166) and is a miniature 12V coil type, with 16A s.p.d.t. contacts, code 60-1015. We see that Display Electronics (2 0208 653 3333) say they have “200,000 from stock’’. Check their web at: www.distel.co.uk. For the prototype, a 9V-0V-9V 100mA mains transformer, with “flying’’ leads, was chosen and also came from Rapid Electronics, code 8880105. A higher current transformer may be used if preferred and your usual component supplier should be able to offer one at a reasonable price. As far as miniature electret microphone inserts go, these are generally listed and carried by such advertisers as ESR Components (2 0191 251 4363), Cricklewood (2 0181 452 0161) and Maplin (2 0870 264 6000).

Our latest “Top Tenner’’ project is a simple Sample-and-Hold add-on for your analogue/digital multimeter and most of the components should be readily available from our components advertisers. The only exception is likely to be the DG419DJ TTL/CMOS compatible analogue switch chip. Any readers who do experience problems with this device, should note that it is currently listed by Maplin (2 0870 264 6000 or www.maplin.co.uk), code AX47B and Electromail (2 01536 304555 or http://rswww.com), code 656-574. If you intend running from a 6V supply, you can use the CA3140 CMOS op.amp, however, as stated in the article, its output cannot swing fully to the positive supply rail; at 6V its output swings from 0V to +4V. If a wider swing is needed, try the CA3130. Alternatively, increase the power supply to 9V or 12V.

Opto-Alarm System The neat looking case used in the Opto-Alarm System project came from the Maplin (2 0870 264 6000 or www.maplin.co.uk) “waterproof box’’ range and is their medium size one, code YM91Y. They also supplied the multi-tone 12V main siren, code JH25C. Most of our components advertisers should be able to provide the ubiquitous ORP12 light dependent resistor (l.d.r.) or its derivative. Depending on the characteristics of the l.d.r. purchased, you may need to adjust the value of resistor R5 as outlined in the article. It may pay readers to shop around for the key-operated switch as prices seem to vary quite considerably.

PLEASE TAKE NOTE PIC Dual-Chan Virtual Scope Oct ’00 Since going to press with the PIC Dual-Chan Virtual Scope, the device specified for IC3, TC55257DPL (and its alternative TC55257DPI), has become obsolete. The author has proved that the NEC device mPD43256BCZ-70LL is a satisfactory replacement and is available from Electromail (the mail order division of RS Components) as code 265-465. Do not attempt to use any other variant of the TC55257 since it may have a different pin configuration. Interface (Temperature PC Interface) Oct ’00 All source code files (including “forms’’) are now available via our FTP site and on the newly introduced “Interface Disk 1’’, see page 868.

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Everyday Practical Electronics, November 2000

STORE YOUR BACK ISSUES IN YOUR WALLET! NOW VOL 2 AVAI LABL E ONLY

£12.45 including VAT and p&p

A new way to buy EPE Back Issues – our wallet-sized CD-ROMs contain back issues from our EPE Online website plus bonus articles, all the relevant PIC software and web links. All this for just £12.45 including postage and packing.

VOL 1 CONTENTS BACK ISSUES – November 1998 to June 1999 (all the projects, features, news, IUs etc. from all eight issues). Note: No advertisem*nts or Free Gifts are included. PIC PROJECT CODES – All the available codes for the PIC based projects published in issues from November 1998 to June 1999. EPE ONLINE STORE – Books, PCBs, Subscriptions, etc.

VOL 2 CONTENTS BACK ISSUES – July 1999 to December 1999 (all the projects, features, news, IUs, etc. from all six issues). Note: No advertisem*nts or Free Gifts are included. PIC PROJECT CODES – All the available codes for the PIC-based projects published in issues from July to December 1999. EPE ONLINE STORE – Books, PCBs, Subscriptions, etc.

EXTRA ARTICLES – ON ALL VOLUMES THE LIFE & WORKS OF KONRAD ZUSE – a brilliant pioneer in the evolution of computers. A bonus article on his life and work written by his eldest son, including many previously unpublished photographs. BASIC SOLDERING GUIDE – Alan Winstanley’s internationally acclaimed fully illustrated guide. UNDERSTANDING PASSIVE COMPONENTS – Introduction to the basic principles of passive components. HOW TO USE INTELLIGENT L.C.Ds, By Julyan Ilett – An utterly practical guide to interfacing and programming intelligent liquid crystal display modules. PhyzzyB COMPUTERS BONUS ARTICLE 1 – Signed and Unsigned Binary Numbers. By Clive “Max” Maxfield and Alvin Brown. PhyzzyB COMPUTERS BONUS ARTICLE 2 – Creating an Event Counter. By Clive “Max” Maxfield and Alvin Brown. INTERGRAPH COMPUTER SYSTEMS 3D GRAPHICS – A chapter from Intergraph’s book that explains computer graphics technology in an interesting and understandable way with full colour graphics.

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BACK ISSUES We can supply back issues of EPE by post, most issues from the past five years are available. An EPE index for the last five years is also available – see order form. Alternatively, indexes are published in the December issue for that year. Where we are unable to provide a back issue a photostat of any one article (or one part of a series) can be purchased for the same price. Issues from Nov. 98 onwards are also available to download from www.epemag.com.

DID YOU MISS THESE? JUNE ’99

JUNE ’00

PROJECTS ) Clipping Video Fader (Starter Project) ) PC Audio Frequency Meter ) Musical Sundial ) PIC Toolkit Mk2–2. FEATURES ) Alan Dower Blumlein ) Circuit Surgery ) Interface ) PhizzyB Computers–8 ) Ingenuity Unlimited ) Edison 3 Review ) Net Work – The Internet.

PROJECTS ) Atmospheric Electricity Detector–1 ) Canute Tide Predictor ) Multi-Channel Transmission System–2 ) Automatic Nightlight. FEATURES ) Teach-In 2000 – Part 8 ) Technology Timelines–5 ) Circuit Surgery ) Interface ) New Technology Update ) Ingenuity Unlimited ) Net Work – The Internet.

JULY ’00

JULY ’99 PROJECTS )12V Lead-acid Battery Tester ) L.E.D. Stroboscope ) EPE Mood Picker ) Intruder Deterrent. FEATURES ) Practical Oscillator Designs–1 ) Practically Speaking ) Circuit Surgery ) Ingenuity Unlimited ) New Technology Update ) Net Work – The Internet.

AUG ’99 PROJECTS ) Ultrasonic Puncture Finder ) Magnetic Field Detective ) Freezer Alarm ) 8Channel Analogue Data Logger–1 ) Sound Activated Switch. FEATURES ) Practical Oscillator Designs–2 ) Power Generation from Pipelines to Pylons–1 ) Ingenuity Unlimited ) Circuit Surgery ) Interface ) Net Work – The Internet.

FEB ’00

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MAR ’00

PROJECTS ) g-Meter ) Camera Shutter Timer PIC-Gen Frequency Generator/Counter ) Atmospheric Electricity Detector–2. FEATURES ) Teach-In 2000–Part 9 ) Practically Speaking ) Ingenuity Unlimited ) Circuit Surgery ) PICO DrDAQ Reviewed ) Net Work – The Internet.

AUG ’00 PROJECTS ) Handy-Amp ) EPE Moodloop )Quiz Game Indicator )Door Protector FEATURES ) Teach-In 2000–Part 10 ) Cave Electronics ) Ingenuity Unlimited ) Circuit Surgery ) Interface ) New Technology Update )Net Work – The Internet.

PROJECTS ) EPE ICEbreaker ) High Performance Regenerative Receiver–1 ) Parking Warning System ) Automatic Train Signal. FEATURES ) Teach-In 2000 – Part 5 ) Practically Speaking ) Technology Timelines–2 ) Ingenuity Unlimited ) Circuit Surgery ) New Technology Update ) Net Work – The Internet.

APRIL ’00 PROJECTS ) Flash Slave ) Garage Link ) MicroPICscope ) High Performance Regenerative Receiver–2. FEATURES ) Teach-In 2000–Part 6 ) Ingenuity Unlimited ) Technology Timelines–3 ) Circuit Surgery ) Interface ) Telcan Home Video ) Net Work – The Internet.

SEPT ’99 PROJECTS ) Loop Aerial SW Receiver ) Child Guard ) 8-Channel Analogue Data Logger–2 ) Variable Dual Power Supply. FEATURES ) Practical Oscillator Designs–3 ) Power Generation from Pipelines to Pylons–2 ) Practically Speaking ) Circuit Surgery ) Ingenuity Unlimited ) New Technology Update ) Net Work.

OCT ’99 PROJECTS ) Interior Lamp Delay ) Mains Cable Detector ) QWL Loudspeaker System ) Micro Power Supply. FEATURES ) PIC16F87x Mini Tutorial ) Practical Oscillator Designs–4 ) Circuit Surgery ) Interface ) Ingenuity Unlimited ) Net Work – The Internet.

NOV ’99 PROJECTS ) Acoustic Probe ) Vibralarm ) Ginormous Stopwatch–1 ) Demister One-Shot. FEATURES ) Teach-In 2000–Part 1 ) Ingenuity Unlimited ) Practically Speaking ) Practical Oscillator Designs–5 ) Circuit Surgery ) New Technology Update ) Net Work – The Internet FREE Identifying Electronic Components booklet.

DEC ’99 PROJECTS ) PIC Micro-Probe ) Magnetic Field Detector ) Loft Guard ) Ginormous Stopwatch – Giant Display–2. FEATURES ) Teach-In 2000–Part 2 ) Practical Oscillator Designs–6 ) Interface ) Ingenuity Unlimited (Special) ) Circuit Surgery ) Network–The Internet ) 1999 Annual Index.

JAN ’00 PROJECTS )Scratch Blanker ) Versatile Burglar Alarm ) Flashing Snowman ) Vehicle Frost Box. FEATURES ) Ingenuity Unlimited ) Teach-In 2000–Part 3 ) Circuit Surgery ) Practically Speaking ) Tina Pro Review ) Net Work – The Internet.

MAY ’00 PROJECTS ) Versatile Mic/Audio Preamplifier ) PIR Light Checker ) Low-Cost Capacitance Meter ) Multi-Channel Transmission System–1. FEATURES ) Teach-In 2000–Part 7 ) Technology Timelines–4 ) Circuit Surgery ) Practically Speaking ) Ingenuity Unlimited ) Net Work – The Internet ) FREE Giant Technology Timelines Chart.

SEPT ’00 PROJECTS ) Active Ferrite Loop Aerial ) Steeplechase Game ) Remote Control IR Decoder ) EPE Moodloop Power Supply. FEATURES ) Teach-In 2000–Part 11 ) New Technology Update ) Circuit Surgery ) Ingenuity Unlimited ) Practically Speaking ) Net Work – The Internet Page.

OCT ’00 PROJECTS ) Wind-Up Torch ) PIC Dual-Chan Virtual Scope ) Fridge/Freezer Alarm ) EPE Moodloop Field Strength Indicator. FEATURES ) Teach-In 2000–Part 12 ) Interface ) Ingenuity Unlimited ) New Technology Update ) Circuit Surgery ) Peak Atlas Component Analyser Review ) Net Work – The Internet Page.

BACK ISSUES ONLY £3.00 each inc. UK p&p. Overseas prices £3.50 each surface mail, £4.95 each airmail. We can also supply issues from earlier years: 1992 (except March, April, June to Sept. and Dec.), 1993 (except Jan. to March, May, Aug., Dec.), 1994 (except April to June, Aug., Oct. to Dec.), 1995 (No Issues), 1996 (except Jan. to May, July, Aug., Nov.), 1997 (except Feb. and March), 1998 (except Jan., March to May, July, Nov., Dec.), 1999. We can also supply back issues of ETI (prior to the merger of the two magazines) for 1998/9 – Vol. 27 Nos 1 to 13 and Vol. 28 No. 1. We are not able to supply any material from ETI prior to 1998. Please put ETI clearly on your order form if you require ETI issues. Where we do not have an issue a photostat of any one article or one part of a series can be provided at the same price.

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1 I enclose cheque/P.O./bank draft to the value of £ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Please charge my Visa/Mastercard £ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Card No. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Card Expiry Date . . . . . . . . . . . . . . . . . . . . . Note: Minimum order for credit cards £5. Please supply name and address of cardholder if different from that shown above. SEND TO: Everyday Practical Electronics, Allen House, East Borough, Wimborne, Dorset BH21 1PF. Tel: 01202 881749. Fax: 01202 841692. E-mail: [emailprotected] Payments must be in £ sterling – cheque or bank draft drawn on a UK bank. Normally supplied within seven days of receipt of order. Send a copy of this form, or order by letter if you do not wish to cut your issue.

Everyday Practical Electronics, November 2000

M11/00

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Special Review

PIC LOGICATOR ROBERT PENFOLD

Learning to program PICs in a very different way, in which flowcharts provide the method. such as the PIC series of processors have huge advantages in many practical applications, but getting M started with these components can be a bit daunting. Many of ICROCONTROLLERS

the problems are probably perceived rather than actual, and producing gadgets based on microcontrollers is not really that difficult. The Logicator is a PIC programmer that aims to make the introduction to the PIC range of processors as painless as possible. To be more precise, it is the software supplied with the programmer that makes life easier for newcomers. The system does include a program that enables the hardware to operate as a conventional PIC programmer, but the main software provides an easy introduction by avoiding the use of any conventional programming language. Instead, the user produces a flowchart, and then the software converts this into PIC code that can be downloaded to a chip in the programmer. Fine in theory, but how does it perform in practice?

Getting Started

Unusually, the main software is supplied on just a single highdensity floppy disk, but two further disks are required for the software that enables the hardware to function as a conventional PIC programmer. The installation process follows along normal Windows lines and it is quite quick and simple. The main program will run under Windows 95, 98, or 2000, but not Windows 3.1 or NT. The ordinary programmer software will run under Windows 9X or 3.1. No minimum hardware requirements are specified, but the software does not seem to be very demanding in this respect. However, a spare serial port is essential to provide the link to the hardware. The hardware consists of a neat programmer unit in a plastic case with a 28-pin ZIF socket for the processors on the top. Markings show the correct positions and orientations for 8-, 18-,

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Fig.1. The first task is to select a processor from the list of supported chips. and 28-pin chips. There are also two l.e.d.s on the top panel of the box, and these are power and activity indicators. The programmer connects to a serial port of the PC via the supplied 9-pin serial lead. An adapter (not included in the outfit) is needed for an old style 25-pin serial port. Power is obtained from the mains adapter supplied with the outfit. Getting the hardware set up is very simple and straightforward.

Easy Flowing

The program has a fairly conventional Windows look with a menu bar at the top and a row of icons just below this to provide shortcuts to the frequently used commands. The Options menu is the first port of call when creating a new flowchart. The PIC Type option brings up a window that provides a list of compatible PIC processors (Fig.1). The right-hand section of the screen has a palette of the basic building elements for the flowcharts. These are simply dragged to the required positions on the main drawing area, which takes up the vast majority of the screen. Initially, there are no flowchart elements in the palette, but a pop-up window enables elements to be added and removed as desired (Fig.2). Double clicking on a cell in the flowchart brings up a small dialogue box that enables the label to be extended. For example, instead of “OUT” you could have something more helpful such as “OUT LED1”. Editing flowcharts is very easy. Once in position, a cell can simply be dragged to a new position if you change your mind. Groups of cells can be selected by drawing a box around them, or cells can be picked individually by holding down the Shift key and left clicking on them. Once selected a group can be dragged around the screen to any desired position. Single cells or groups can be deleted by selecting the appropriate cell or cells and pressing the Delete key. The Edit

Everyday Practical Electronics, November 2000

Fig.2. Elements can be added to or removed from the command list at the right-hand side of the screen.

Fig.3. It is easy to navigate around a drawing using the Map facility.

menu provides the usual cut, copy, paste, and delete functions, which will work with individual elements or groups of them. Routes (the lines between cells) are drawn by holding down the right mouse button and then dragging the lines from one cell to another. The drawing area can be viewed at a wide range of zoom levels, and a map facility (Fig.3) makes it easy to navigate around charts when using high zoom levels. The drawing area can be used with or without guidelines to help with the placement of the elements.

programming software provided with the system. Anyone making the transition from the Logicator software to conventional assembly language will have a lot to learn, but Logicator programs have the normal programming elements. There are loops, conditional commands,variables so that a loop can be performed a certain number of times, macros(subroutines), etc. Events and interrupts are catered for, as is a timed SLEEP mode. Flowchart methods of programming can become unwieldy, but the Logicator software provides a good compromise between straightforward operation on one hand and functionality on the other.

Programming

The process of drawing and editing flow charts is easy enough, but producing charts that actually get a PIC processor to do something worthwhile is inevitably a bit more difficult. With most of the cells in a chart it is necessary to provide more information in order to get exactly the required function. For example, an Outputs block controls an output port, but the programmer must indicate the required state of each bit of the port. Where appropriate, double clicking on a cell brings up a small dialogue box that enables its characteristics to be controlled. Fig.4 shows the Cell Details window for an output port. Left clicking enables each bit to be cycled through logic 0, logic 1, or no change (indicated by a dot in the control panel). Each type of cell has its own characteristics. With a Wait cell the delay in seconds can be specified, with a Sound cell the pitch and duration of the signal are set, and so on. This system enables programs to be produced very easily, but it inevitably involves some compromises. The PIC processors can have each pin of a port individually set as an input or an output, but the Logicator software only supports one preset port configuration for most chips. With a few there are two port options to choose from. This means that you have to settle for something quite basic, such as one five-bit input port and one eight-bit output type with the PIC16F84 for instance. Some analogue inputs are provided for chips that have a built-in analogue to digital converter. Of course, the Logicator software is not intended as an alternative to conventional PIC programming, and is designed to be an easy introduction to using these devices. Having exhausted the possibilities of the Logicator software the user can move on to conventional assembly language programming and the standard

Fig.4. The Digital Panel shows the states of the input and output lines while an emulation is running.

Everyday Practical Electronics, November 2000

Testing Time

Having completed a flow chart it can be tested using the emulation mode. The block currently being processed is highlighted, and there are optional windows that can be brought up to monitor the contents of the EEPROM, variables, and the ports. The screen in Fig.4 shows a simple l.e.d. flashing program being tested, with the Digital Panel being used to show the states of the input and output lines. A variable delay can be used between cells to slow things down to the point where the action of the program can be followed properly. The emulation mode should bring to light any major bugs so that they can be fixed prior to downloading programs to PIC chips. Once you are completely satisfied that the software is working properly it is downloaded to the processor by selecting Program PIC from the Options menu. Downloading is done as a single operation with no separate compilation process. If everything is set up correctly the software will be immediately downloaded to the chip, and the whole process is very quick and easy. The chip is then ready for the “acid test”. The conventional programmer software (Fig.5) has the usual pushbutton controls, etc. that make it easy to select the required options and download the software. Only a limited range of processors are supported at present, but hopefully more will soon be accommodated. This program can be used to download HEX files generated by the Logicator program.

Fig.5. The conventional programmer software is easy to set up and operate.

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The A4 ring bound instruction manual is not particularly long at 56 pages, but it covers a fair amount of ground. In addition to getting everything set up correctly and building flowcharts, it also covers basic circuits for the various PIC chips that can be used with the system. These provide supply connections, reset circuits, clock circuit (a 4MHz ceramic resonator must be used), and connections to devices such as l.e.d.s, lamps, counters, and sounders. The manual is clear, well written, and easy to follow.

Ice

Economatics produce a PIC emulator for use with the Logicator system. When using the emulator things are handled in the normal way up to the point where the software is downloaded to the PIC chip. Instead of using the programmer, the emulator is connected to the serial port. The emulator uses the same lead and power supply unit as the programmer. The emulator has 8-, 18-, and 28way sockets that connect to the prototype circuit via a cable and header plug. The header plug takes the place of the PIC processor in the prototype circuit. Only an 18-way cable and header plug is provided with the emulator.

The emulator does not provide power to the test circuit, which must therefore have its own power supply where appropriate. The emulator does not use any clock circuit in the test circuit, but instead uses its own 4MHz clock generator. In order to run a simulation in direct mode you simply select the Run option from the main menu. The program is then emulated on screen and in the test circuit. Downloading a program to the emulator is handled in exactly the same way as downloading a program to a chip in the programmer. Once downloaded, the emulator automatically switches to the remote run mode and runs the program. Using the emulator and a solderless breadboard it is possible to thoroughly check designs before downloading the software to a PIC processor. For educational purposes and experimenting it is possible to dispense with the PIC chips altogether, with the emulator being used as an alternative.

Conclusion

During the brief test period the software proved to be entirely stable, and the hardware did what it was supposed to do. The hardware seems to be well made and quite tough, which it needs to be, as the PICLogicator system is used extensively in UK schools to teach Design and Technology. This system is not really suitable for developing complex equipment based on PIC processors, but it is not intended for this role. It has been designed as an easy introduction to using PIC processors, and it fulfils this role very well. Having exhausted the possibilities of the flowchart method of programming, the user can move on to the “real thing” by using a PIC assembler to produce HEX files that can be downloaded to the PIC chips, using the programmer and the supplied software. No assembler is supplied with the system, but free PIC assemblers are readily available from web sites. Neither the Logicator system nor the emulator is particularly cheap, but the prices are quite reasonable. Although aimed The PIC Emulator used with the Logicator system. primarily at educational establishments, the Logicator system and the emulator are also There are two operating modes available. In the direct mode the well suited to electronic hobbyists requiring an easy way of getting input and output ports of the emulator hardware are controlled and to grips with PIC processors. With no obvious drawbacks and read directly by the Logicator software. If the remote run mode is plenty going for it, the Logicator can certainly be recommended used the program is downloaded to the emulator’s EEPROM for both educational and hobbyist use. memory, and the emulator then operates as a stand alone unit that The PIC-Logicator system costs £149.95. The Emulator costs requires no further control from the host PC. £119.95. Both prices include VAT and UK carriage. For further The emulator is in the form of an uncased board that has a information contact Economatics, Dept EPE, Epic House, power/status l.e.d. plus reset, pause, and mode controls Darnall Road, Sheffield S9 5AA, UK. Tel:0114 281 3311. Fax: provided by miniature pushbutton switches. The status l.e.d. 0114 243 9306. There is also a web site devoted to the PICgoes from red to green when the unit is switched into the Logicator system and providing an interactive software demo at remote run mode. www.pic-logicator.com.

N. R. BARDWELL L TD (EPE) 100 75 50 10 10 4 50 12 25 25 50 25 20 25 30 20 30 30 30 30 25 30 30 20 100 100 12 80 80

860

Signal Diodes 1N4148 . . . . . . . . . . . . .£1.00 Rectifier Diodes 1N4001 . . . . . . . . . . .£1.00 Rectifier Diodes 1N4007 . . . . . . . . . . .£1.00 W01 Bridge Rectifiers . . . . . . . . . . . . .£1.00 555 Timer I.C.s . . . . . . . . . . . . . . . . . .£1.00 741 Op Amps . . . . . . . . . . . . . . . . . . .£1.00 Assorted Zener Diodes 400mW . . . . . .£1.00 Assorted 7-segment Displays . . . . . . . .£1.00 5mm l.e.d.s, red, green or yellow . . . . .£1.00 3mm l.e.d.s, red, green or yellow . . . . .£1.00 Axial l.e.d.s, 2mcd red Diode Package .£1.00 Asstd. High Brightness l.e.d.s, var cols .£1.00 BC182L Transistors . . . . . . . . . . . . . . .£1.00 BC212L Transistors . . . . . . . . . . . . . . .£1.00 BC237 Transistors . . . . . . . . . . . . . . . .£1.00 BC327 Transistors . . . . . . . . . . . . . . . .£1.00 BC328 Transistors . . . . . . . . . . . . . . . .£1.00 BC547 Transistors . . . . . . . . . . . . . . . .£1.00 BC548 Transistors . . . . . . . . . . . . . . . .£1.00 BC549 Transistors . . . . . . . . . . . . . . . .£1.00 BC557 Transistors . . . . . . . . . . . . . . . .£1.00 BC558 Transistors . . . . . . . . . . . . . . . .£1.00 BC559 Transistors . . . . . . . . . . . . . . . .£1.00 2N3904 Transistors . . . . . . . . . . . . . . .£1.00 1nf 50V wkg Axial Capacitors . . . . . . .£1.00 4N7 50V wkg Axial Capacitors . . . . . .£1.00 1uf 250V encapsulated radial plastic cased capacitors . . . . . . . . . . . . . . . . .£1.00 Asstd capacitors electrolytic- . . . . . . . .£1.00 Asstd. capacitors 1nF to 1mF . . . . . . . .£1.00

200 50 50 50 80 10 24 8 20 10 100 80 30 10 40 20 20 100 10

Asstd. disc ceramic capacitors . . . . . . .£1.00 Asstd. Skel Presets (sm, stand, cermet) £1.00 Asstd. RF chokes (inductors) . . . . . . . .£1.00 Asstd. grommets . . . . . . . . . . . . . . . . .£1.00 Asstd. solder tags, p/conns, terminals .£1.00 Asstd. crystals – plug in . . . . . . . . . . . .£1.00 Asstd. coil formers . . . . . . . . . . . . . . . .£1.00 Asstd. dil switches . . . . . . . . . . . . . . . .£1.00 Miniature slide switches sp/co . . . . . . .£1.00 Standard slide switches dp/dt . . . . . . . .£1.00 Asstd. beads (ceramic, teflon, fish spine) £1.00 Asstd. small stand offs, l/throughs etc .£1.00 Asstd. dil sockets up to 40 way . . . . . . .£1.00 TV coax plugs, plastic . . . . . . . . . . . . .£1.00 metres very thin connecting wire, red . .£1.00 1in. glass reed switches . . . . . . . . . . . .£1.00 Magnetic ear pips with lead and plug .£1.00 Any one value 1/4W 5% cf resistors range 1R to 10M . . . . . . . . . . . . . . . . . . . . . .£0.45 7812 Voltage Regulators . . . . . . . . . . .£1.00

Prices include VAT. Postage £1.65. 44p stamp for Lists

288 Abbeydale Road, Sheffield S7 1FL Phone (0114) 2552886 Fax (0114) 2500689

DIGITAL TEST METER Built-in transistor test socket and diode test position. DC volts 200mV to 1000V. AC volts 200V to 750V. DC current 200mA to 10A. Resistance 200 ohms to 2000K ohms.

£6.99

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DIRECT BOOK SERVICE NEW SOFTBACK EDITION

The books listed have been selected by Everyday Practical Electronics editorial staff as being of special interest to everyone involved in electronics and computing. They are supplied by mail order to your door. Full ordering details are given on the last book page.

EPE books

Only £14.99 THE INVENTOR OF STEREO – THE LIFE AND WORKS OF ALAN DOWER BLUMLEIN Robert Charles Alexander This book is the definitive study of the life and works of one of Britain’s most important inventors who, due to a cruel set of circ*mstances, has all but been overlooked by history. Alan Dower Blumlein led an extraordinary life in which his inventive output rate easily surpassed that of Edison, but whose early death during the darkest days of World War Two led to a shroud of secrecy which has covered his life and achievements ever since. His 1931 Patent for a Binaural Recording System was so revolutionary that most of his contemporaries regarded it as more than 20 years ahead of its time. Even years after his death, the full magnitude of its detail had not been fully utilized. Among his 128 patents are the principal electronic circuits critical to the development of the world’s first elecronic television system. During his short working life, Blumlein produced patent after patent breaking entirely new ground in electronic and audio engineering. During the Second World War, Alan Blumlein was deeply engaged in the very secret work of radar development and contributed enormously to the system eventually to become ‘H2S’ – blind-bombing radar. Tragically, during an experimental H2S flight in June 1942, the Halifax bomber in which Blumlein and several colleagues were flying, crashed and all aboard were killed. He was just days short of his thirty-ninth birthday.

420 pages

Order code NE32

£14.99

TEACH-IN No. 7. ANALOGUE AND DIGITAL ELECTRONICS COURSE (published by Everyday Practical Electronics) Alan Winstanley and Keith Dye B.Eng(Tech)AMIEE This highly acclaimed EPE Teach-In series, which included the construction and use of the Mini Lab and Micro Lab test and development units, has been put together in book form. An interesting and thorough tutorial series aimed specifically at the novice or complete beginner in electronics. The series is designed to support those undertaking either GCSE Electronics or GCE Advanced Levels, and starts with fundamental principles. If you are taking electronics or technology at school or college, this book is for you. If you just want to learn the basics of electronics or technology you must make sure you see it. Teach-In No. 7 will be invaluable if you are considering a career in electronics or even if you are already training in one. The Mini Lab and software enable the construction and testing of both demonstration and development circuits. These learning aids bring electronics to life in an enjoyable and interesting way: you will both see and hear the electron in action! The Micro Lab microprocessor add-on system will appeal to higher level students and those developing microprocessor projects.

152 pages

Order code TI7

£3.95

project construction PRACTICAL REMOTE CONTROL PROJECTS Owen Bishop Provides a wealth of circuits and circuit modules for use in remote control systems of all kinds; ultrasonic, infrared, optical fibre, cable and radio. There are instructions for building fourteen novel and practical remote control projects. But this is not all, as each of these projects provides a model for building dozens of other related circuits by simply modifying parts of the design slightly to suit your own requirements. This book tells you how. Also included are techniques for connecting a PC to a remote control system, the use of a microcontroller in remote control, as exemplified by the BASIC Stamp, and the application of ready-made type-approved 418MHz radio transmitter and receiver modules to remote control systems. 160 pages Order code BP413 £5.99 PRACTICAL ELECTRONIC MODEL RAILWAY PROJECTS R. A. Penfold The aim of this book is to provide the model railway enthusiast with a number of useful but reasonably simple projects that are easily constructed from readily available components. Stripboard layouts and wiring diagrams are provided for each project. The projects covered include: constant voltage controller; pulsed controller; pushbutton pulsed controller; pulsed controller with simulated inertia, momentum and braking; automatic signals; steam whistle sound effect; two-tone horn sound effect; automatic two-tone horn effect; automatic chuffer. The final chapter covers the increasingly popular subject of using a computer to control a model railway layout, including circuits for computer-based controllers and signalling systems.

151 pages

Order code BP384

£4.99

A PRACTICAL INTRODUCTION TO SURFACE MOUNT DEVICES Bill Mooney This book takes you from the simplest possible starting point to a high level of competence in handworking with surface mount devices (SMD’s). The wider subject of SM technology is also introduced, so giving a feeling for its depth and fascination. Subjects such as p.c.b. design, chip control, soldering techniques and specialist tools for SM are fully explained and developed as the book progresses. Some useful constructional projects are also included. Whilst the book is mainly intended as an introduction it is also an invaluable reference book, and the browser should find it engrossing. 120 pages Order code BP411 £4.99

FAULT-FINDING ELECTRONIC PROJECTS R. A. Penfold Starting with mechanical faults such as dry joints, short-circuits etc, coverage includes linear circuits, using a meter to make voltage checks, signal tracing techniques and fault finding on logic circuits. The final chapter covers ways of testing a wide range of electronic components, such as resistors, capacitors, operational amplifiers, diodes, transistors, SCRs and triacs, with the aid of only a limited amount of test equipment. The construction and use of a Tristate Continuity Tester, a Signal Tracer, a Logic Probe and a CMOS Tester are also included. 136 pages Order code BP391 £4.99 TEST EQUIPMENT CONSTRUCTION R. A. Penfold This book describes in detail how to construct some simple and inexpensive but extremely useful, pieces of test equipment. Stripboard layouts are provided for all designs, together with wiring diagrams where appropriate, plus notes on construction and use. The following designs are included:AF Generator, Capacitance Meter, Test Bench Amplifier, AF Frequency Meter, Audio Mullivoltmeter, Analogue Probe, High Resistance Voltmeter, CMOS Probe, Transistor Tester, TTL Probe.The designs are suitable for both newcomers and more experienced hobbyists. 104 pages Order code BP248 £3.99 HOW TO DESIGN AND MAKE YOUR OWN P.C.B.s R. A. Penfold Deals with the simple methods of copying printed circuit board designs from magazines and books, and covers all aspects of simple p.c.b. construction including photographic methods and designing your own p.c.b.s. 66 pages Order code BP121 £3.99 ELECTRONIC PROJECT BUILDING FOR BEGINNERS R. A. Penfold This book is for complete beginners to electronic project building. It provides a complete introduction to the practical side of this fascinating hobby, including the following topics: Component identification, and buying the right parts; Resistor colour codes, capacitor value markings, etc; Advice on buying the right tools for the job; Soldering, with advice on how to produce good joints and avoid “dry’’ joints; Making easy work of the hard wiring; Construction methods, including stripboard, custom printed circuit boards, plain matrix board, surface mount boards and wire-wrapping; Finishing off, and adding panel labels; Getting “problem” projects to work, including simple methods of fault-finding; In fact everything you need to know in order to get started in this absorbing and creative hobby. 135 pages Order code BP392 £4.95

Everyday Practical Electronics, November 2000

FOR A FURTHER SELECTION OF BOOKS SEE THE NEXT TWO ISSUES OF EPE. Note our UK postage costs just £2.00 no matter how many books you order!

radio / tv video ELECTRONIC PROJECTS FOR VIDEO ENTHUSIASTS R. A. Penfold This book provides a number of practical designs for video accessories that will help you get the best results from your camcorder and VCR. All the projects use inexpensive components that are readily available, and they are easy to construct. Full construction details are provided, including stripboard layouts and wiring diagrams. Where appropriate, simple setting up procedures are described in detail; no test equipment is needed. The projects covered in this book include: Four channel audio mixer, Four channel stereo mixer, Dynamic noise limiter (DNL), Automatic audio fader, Video faders, Video wipers, Video crispener, Mains power supply unit. 109 pages Order code BP356 £4.95 SETTING UP AN AMATEUR RADIO STATION I. D. Poole The aim of this book is to give guidance on the decisions which have to be made when setting up any amateur radio or short wave listening station. Often the experience which is needed is learned by one’s mistakes, however, this can be expensive. To help overcome this, guidance is given on many aspects of setting up and running an efficient station. It then proceeds to the steps that need to be taken in gaining a full transmitting licence. Topics covered include: The equipment that is needed; Setting up the shack; Which aerials to use; Methods of construction; Preparing for the licence. An essential addition to the library of all those taking their first steps in amateur radio. 86 pages Order code BP300 £3.95 EXPERIMENTAL ANTENNA TOPICS H. C. Wright Although nearly a century has passed since Marconi’s first demonstration or radio communication, there is still research and experiment to be carried out in the field of antenna design and behaviour. The aim of the experimenter will be to make a measurement or confirm a principle, and this can be done with relatively fragile, short-life apparatus. Because of this, devices described in this book make liberal use of cardboard, cooking foil, plastic bottles, cat food tins, etc. These materials are, in general, cheap to obtain and easily worked with simple tools, encouraging the trial-and-error philosophy which leads to innovation and discovery. Although primarily a practical book with text closely supported by diagrams, some formulae which can be used by straightforward substitution and some simple graphs have also been included. 72 pages Order code BP278 £3.50 25 SIMPLE INDOOR AND WINDOW AERIALS E. M. Noll Many people live in flats and apartments or other types of accommodation where outdoor aerials are prohibited, or a lack of garden space etc. prevents aerials from being erected.This does not mean you have to forgo shortwave-listening, for even a 20-foot length of wire stretched out along the skirting board of a room can produce acceptable results. However, with some additional effort and experimentation one may well be able to improve performance further. This concise book tells the story, and shows the reader how to construct and use 25 indoor and window aerials that the author has proven to be sure performers. Much information is also given on shortwave bands, aerial directivity, time zones, dimensions etc. 50 pages Order code BP136 £1.75

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TWO EXCITING BOOKS Specially imported by EPE

Bebop To The Boolean Boogie

Bebop Bytes Back By Clive “Max’’ Maxfield and Alvin Brown ORDER CODE BEB2 £29.95

By Clive (call me Max) Maxfield ORDER CODE BEB1 £24.95

An Unconventional Guide To Computers

An Unconventional Guide to Electronics Fundamentals, Components and Processes The Foreword by Pete Waddell, Editor, Printed Circuit Design reads: “Personally, I think that the title of this tome alone (hmmm, a movie?) should provide some input as to what you can expect. But, for those who require a bit more: be forewarned, dear reader, you will probably learn far more than you could hope to expect from Bebop to the Boolean Boogie, just because of the unique approach Max has to technical material. The author will guide you from the basics through a minefield of potentially boring theoretical mish-mash, to a Nirvana of understanding. You will not suffer that fate familiar to every reader: re-reading paragraphs over and over wondering what in the world the author was trying to say. For a limey, Max shoots amazingly well and from the hip, but in a way that will keep you interested and amused. If you are not vigilant, you may not only learn something, but you may even enjoy the process. The only further advice I can give is to ‘expect the unexpected’.’’ This book gives the “big picture’’ of digital electronics. This indepth, highly readable, up-to-the-minute guide shows you how electronic devices work and how they’re made. You’ll discover how transistors operate, how printed circuit boards are fabricated, and what the innards of memory ICs look like. You’ll also gain a working knowledge of Boolean Algebra and Karnaugh Maps, and understand what Reed-Muller logic is and how it’s used. And there’s much, MUCH more (including a recipe for a truly great seafood gumbo!). Hundreds of carefully drawn illustrations clearly show the important points of each topic. The author’s tongue-in-cheek British humor makes it a delight to read, but this is a REAL technical book, extremely detailed and accurate. A great reference for your own shelf, and also an ideal gift for a friend or family member who wants to understand what it is you do all day. . . .

By importing these books ourselves we have managed to make them available in the UK at an exceptional price.

Plus FREE CD-ROM which includes: Fully Functional Internet-Ready Virtual Computer with Interactive Labs The Foreword by Lee Felsenstein reads: “1. The more time you spend with this book and its accompanying CD-ROM, the more you’ll get out of it. Skimming through it won’t take you where you want to go. Paying serious attention, on the other hand, will teach you more about computers than you can imagine. (You might also see a few beautiful sunrises.) 2. The labs work on two levels: on and under the surface. When you’re performing the labs you’ll need to look for patterns that build up from individual events. 3. When you’re done, you won’t look any different. You won’t get a trophy or a certificate to hang on your wall. You’ll have some knowledge, and some skill, and you’ll be ready to find more knowledge and develop more skill. Much of this will be recognisable only to someone who has the same knowledge and skill.’’ This follow-on to Bebop to the Boolean Boogie is a multimedia extravaganza of information about how computers work. It picks up where “Bebop I’’ left off, guiding you through the fascinating world of computer design . . . and you’ll have a few chuckles, if not belly laughs, along the way. In addition to over 200 megabytes of mega-cool multimedia, the accompanying CDROM (for Windows 95 machines only) contains a virtual microcomputer, simulating the motherboard and standard computer peripherals in an extremely realistic manner. In addition to a wealth of technical information, myriad nuggets of trivia, and hundreds of carefully drawn illustrations, the book contains a set of lab experiments for the virtual microcomputer that let you recreate the experiences of early computer pioneers. If you’re the slightest bit interested in the inner workings of computers, then don’t dare to miss this one!

Audio and Music VALVE & TRANSISTOR AUDIO AMPLIFIERS John Linsley Hood This is John Linsley Hood’s greatest work yet, describing the milestones that have marked the development of audio amplifiers since the earliest days to the latest systems. Including classic amps with valves at their heart and exciting new designs using the latest components, this book is the complete world guide to audio amp design. Contents: Active components; Valves or vacuum tubes; Solid-state devices; Passive components; Inductors and transformers; Capacitors, Resistors, Switches and electrical contacts; Voltage amplifier stages using valves; Valve audio amplifier layouts; Negative feedback; Valve operated power amplifiers; Solid state voltage amplifiers; Early solid-state audio amplifiers; Contemporary power amplifier designs; Preamplifiers; Power supplies (PSUs); Index. 250 pages Order code NE24 £19.99 AUDIO AMPLIFIER PROJECTS R. A. Penfold A wide range of useful audio amplifier projects, each project features a circuit diagram, an explanation of the circuit operation and a stripboard layout diagram. All constructional details are provided along with a shopping list of components, and none of the designs requires the use of any test equipment in order to set up properly. All the projects are designed for straightforward assembly on simple circuit boards. Circuits include: High impedance mic preamp, Low impedance mic preamp, Crystal mic preamp, Guitar and

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GP preamplifier, Scratch and rumble filter, RIAA preamplifier, Tape preamplifier, Audio limiter, Bass and treble tone controls, Loudness filter, Loudness control, Simple graphic equaliser, Basic audio mixer, Small (300mW) audio power amp, 6 watt audio power amp, 20/32 watt power amp and power supply, Dynamic noise limiter. A must for audio enthusiasts with more sense than money! 116 pages Order code PC113 £9.95 MAKING MUSIC WITH DIGITAL AUDIO Ian Waugh In this practical and clearly written book, Ian Waugh explains all aspects of the subject from digital audio basics to putting together a system to suit your own music requirements. Using the minimum of technical language, the book explains exactly what you need to know about: Sound and digital audio, Basic digital recording principles, Sample rates and resolutions, Consumer sound cards and dedicated digital audio cards. On a practical level you will learn about: sample editing, digital multi-tracking, digital FX processing, integrating MIDI and digital audio, using sample CDs, mastering to DAT and direct to CD, digital audio and Multimedia. This book is for every musician who wants to be a part of the most important development in music since the invention of the gramophone. It’s affordable, it’s flexible, it’s powerful and it’s here now! It’s digital and it’s the future of music making.

256 pages

Order code PC114

POSTAGE You only pay

£2.00

per order (UK postage) NO MATTER HOW MANY BOOKS YOU ORDER Overseas Readers see ORDERING DETAILS on the next page for overseas postage prices

£14.95

Everyday Practical Electronics, November 2000

circuits and design AN INTRODUCTION TO PIC MICROCONTROLLERS Robert Penfold Designing your own PIC based projects may seem a daunting task, but it is really not too difficult providing you have some previous experience of electronics. The PIC processors have plenty of useful features, but they are still reasonably simple and straightforward to use. This book should contain everything you need to know. Topics covered include: the PIC register set; numbering systems; bitwise operations and rotation; the PIC instruction set; using interrupts; using the analogue to digital converter; clock circuits; using the real time clock counter (RTCC); using subroutines; driving seven segment displays. 166 pages Order code BP394 £5.99 PRACTICAL OSCILLATOR CIRCUITS A. Flind Extensive coverage is given to circuits using capacitors and resistors to control frequency. Designs using CMOS, timer i.c.s and op.amps are all described in detail, with a special chapter on ``waveform generator’’ i.c.s. Reliable “white’’ and “pink’’ noise generator circuits are also included. Various circuits using inductors and capacitors are covered, with emphasis on stable low frequency generation. Some of these are amazingly simple, but are still very useful signal sources. Crystal oscillators have their own chapter. Many of the circuits shown are readily available special i.c.s for simplicity and reliability, and offer several output frequencies. Finally, complete constructional details are given for an audio sinewave generator. 133 pages Order code BP393 £4.99 PRACTICAL ELECTRONIC CONTROL PROJECTS Owen Bishop Explains electronic control theory in simple, non-mathematical terms and is illustrated by 30 practical designs suitable for the student or hobbyist to build. Shows how to use sensors as input to the control system, and how to provide output to lamps, heaters, solenoids, relays and motors. Computer based control is explained by practical examples that can be run on a PC. For stand-alone systems, the projects use microcontrollers, such as the inexpensive and easy-to-use Stamp BASIC microcontroller.

198 pages

Order code BP377

£5.99

PRACTICAL ELECTRONICS HANDBOOK – Fifth Edition. Ian Sinclair Contains all of the everyday information that anyone working in electronics will need. It provides a practical and comprehensive collection of circuits, rules of thumb and design data for professional engineers, students and enthusaists, and therefore enough background to allow the understanding and development of a range of basic circuits. Contents: Passive components, Active discrete components, Circuits, Linear I.C.s, Energy conversion components, Digital I.C.s, Microprocessors and microprocessor

systems, Transferring digital data, Digital-analogue conversions, Computer aids in electronics, Hardware components and practical work, Microcontrollers and PLCs, Digital broadcasting, Electronic security. 440 pages Order code NE21 £14.99 COIL DESIGN AND CONSTRUCTIONAL MANUAL B. B. Babani A complete book for the home constructor on “how to make’’ RF, IF, audio and power coils, chokes and transformers. Practically every possible type is discussed and calculations necessary are given and explained in detail. Although this book is now twenty years old, with the exception of toroids and pulse transformers little has changed in coil design since it was written.

96 pages

Order code 160

OPERATIONAL AMPLIFIER USER’S HANDBOOK R. A. Penfold The first part of this book covers standard operational amplifer based “building blocks’’ (integrator, precision rectifier, function generator, amplifiers, etc), and considers the ways in which modern devices can be used to give superior performance in each one. The second part describes a number of practical circuits that exploit modern operational amplifiers, such as high slew-rate, ultra low noise, and low input offset devices. The projects include: Low noise tape preamplifier, low noise RIAA preamplifier, audio power amplifiers, d.c. power controllers, opto-isolator audio link, audio millivolt meter, temperature monitor, low distortion audio signal generator, simple video fader, and many more. 120 pages Order code BP335 £4.95

£3.99

OPTOELECTRONICS CIRCUITS MANUAL R. M. Marston A useful single-volume guide to the optoelectronics device user, specifically aimed at the practical design engineer, technician, and the experimenter, as well as the electronics student and amateur. It deals with the subject in an easy-to-read, down-to-earth, and nonmathematical yet comprehensive manner, explaining the basic principles and characteristics of the best known devices, and presenting the reader with many practical applications and over 200 circuits. Most of the i.c.s and other devices used are inexpensive and readily available types, with universally recognised type numbers.

A BEGINNERS GUIDE TO CMOS DIGITAL ICs R. A. Penfold Getting started with logic circuits can be difficult, since many of the fundamental concepts of digital design tend to seem rather abstract, and remote from obviously useful applications. This book covers the basic theory of digital electronics and the use of CMOS integrated circuits, but does not lose sight of the fact that digital electronics has numerous “real world’’ applications. The topics covered in this book include: the basic concepts of logic circuits; the functions of gates, inverters and other logic “building blocks’’; CMOS logic i.c. characteristics, and their advantages in practical circuit design; oscillators and monostables (timers); flip/flops, binary dividers and binary counters; decade counters and display drivers.

182 pages

119 pages

Order code NE14

£14.99

Order code BP333

£4.95

audio and music INTRODUCTION TO DIGITAL AUDIO (Second Edition) Ian Sinclair The compact disc (CD) was the first device to bring digital audio methods into the home. This development has involved methods and circuits that are totally alien to the technician or keen amateur who has previously worked with audio circuits. The principles and practices of digital audio owe little or nothing to the traditional linear circuits of the past, and are much more comprehensible to today’s computer engineer than the older generation of audio engineers. This book is intended to bridge the gap of understanding for the technician and enthusiast. The principles and methods are explained, but the mathematical background and theory is avoided, other than to state the end product. 128 pages Order code PC102 £7.95 PROJECTS FOR THE ELECTRIC GUITAR J. Chatwin This book is for anyone interested in the electric guitar. It explains how the electronic functions of the instrument work together, and includes information on

BOOK ORDERING DETAILS Our postage price is the same no matter how many books you order, just add £2.00 to your total order for postage and packing (overseas readers add £4 for countries in the EEC, or add £7 for all countries outside the EEC, surface mail postage) and send a PO, cheque, international money order (£ sterling only) made payable to Direct Book Service or credit card details, Visa or Mastercard – minimum credit card order is £5 – to: DIRECT BOOK SERVICE, ALLEN HOUSE, EAST BOROUGH, WIMBORNE, DORSET BH21 1PF Books are normally sent within seven days of receipt of order, but please allow 28 days for delivery (more for overseas orders). Please check price and availability (see latest issue of Everyday Practical Electronics) before ordering from old lists. For a further selection of books see the next two issues of EPE. DIRECT BOOK SERVICE IS A DIVISION OF WIMBORNE PUBLISHING LTD. Tel 01202 881749 Fax 01202 841692. E-mail:[emailprotected]

BOOK ORDER FORM Full name: ............................................................................................................................................... Address: .................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. .............................................. Post code: ........................... Telephone No: ............................................. Signature: ................................................................................................................................................ I enclose cheque/PO payable to DIRECT BOOK SERVICE for £ ................................................... Please charge my Visa/Mastercard £ ...................................... Card expiry date ............................ Card Number .......................................................................................................................................... Please send book order codes: ................................................................................................................................................................. Please continue on separate sheet of paper if necessary

Everyday Practical Electronics, November 2000

the various pickups and transducers that can be fitted. There are complete circuit diagrams for the major types of instrument, as well as a selection of wiring modifications and pickup switching circuits. These can be used to help you create your own custom wiring. Along with the electric guitar, sections are also included relating to acoustic instruments. The function of specialised piezoelectric pickups is explained and there are detailed instructions on how to make your own contact and bridge transducers. The projects range from simple preamps and tone boosters, to complete active controls and equaliser units. 92 pages Order code BP358 £4.95 VALVE AMPLIFIERS Second Edition. Morgan Jones This book allows those with a limited knowledge of the field to understand both the theory and practice of valve audio amplifier design, such that they can analyse and modify circuits, and build or restore an amplifier. Design principles and construction techniques are provided so readers can devise and build from scratch, designs that actually work. The second edition of this popular book builds on its main strength – exploring and illustrating theory with practical applications. Numerous new sections include: output transformer problems; heater regulators; phase splitter analysis; and component technology. In addition to the numerous amplifier and preamplifier circuits, three major new designs are included: a low-noise single-ended LP stage, and a pair of high voltage amplifiers for driving electrostatic transducers directly – one for headphones, one for loudspeakers.

488 pages

Order code NE33

£24.99

VALVE RADIO AND AUDIO REPAIR HANDBOOK Chas Miller This book is not only an essential read for every professional working with antique radio and gramophone equipment, but also dealers, collectors and valve technology enthusiasts the world over. The emphasis is firmly on the practicalities of repairing and restoring, so technical content is kept to a minimum, and always explained in a way that can be followed by readers with no background in electronics. Those who have a good grounding in electronics, but wish to learn more about the practical aspects, will benefit from the emphasis given to hands-on repair work, covering mechanical as well as electrical aspects of servicing. Repair techniques are also illustrated throughout. A large reference section provides a range of information compiled from many contemporary sources, and includes specialist dealers for valves, components and complete receivers.

288 pages

Order code NE34

£19.99

LOUDSPEAKERS FOR MUSICIANS Vivan Capel This book contains all that a working musician needs to know about loudspeakers; the different types, how they work, the most suitable for different instruments, for cabaret work, and for vocals. It gives tips on constructing cabinets, wiring up, when and where to use wadding, and when not to, what fittings are available, finishing, how to ensure they travel well, how to connect multispeaker arrays and much more. Ten practical enclosure designs with plans and comments are given in the last chapter, but by the time you’ve read that far you should be able to design your own!

164 pages

Order code BP297

£4.99

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Constructional Project

HANDCLAP SWITCH TOM WEBB

Let there be light – quick as the clappers! HIS circuit has been designed to give you an easy life. No need to bend down to turn on awkwardly positioned switches, just clap your hands and the controlled appliance will be turned on for you. The block diagram in Fig.1 shows how the circuit is split up into separate sections. The sound made by a handclap is picked up by an electret microphone, amplified by an op.amp, half-wave rectified and then cleaned up by a Schmitt trigger. There is then a switched choice of either using the Timer circuit, which turns on a relay for a predetermined time set by a potentiometer, or using the Latching circuit, which turns on the relay until another handclap is received to turn it off.

T

CIRCUIT DIAGRAM

The circuit diagram for the Handclap Switch is shown in Fig.2. The electret microphone is shown as MIC1 and is powered via resistor R1. Incoming sounds are a.c. coupled by C1 and fed to the non-inverting input (pin 3) of op.amp IC1. This input is d.c. biased at half the supply voltage by the potential divider formed by resistors R2 and R3. The op.amp’s gain is set at about 471, as determined by the values of resistors R4 and R5, i.e. (R4/R5) + 1. Capacitor C2

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provides d.c. stability of the feedback path. The amplified output signal at IC1 pin 6 is a.c. coupled by C3 and fed to the preset amplitude control VR1. From the wiper of VR1, the signal is rectified by the diode pump circuit comprising C4 and diodes D1 and D2. The resulting output voltage from D2 is smoothed by the CR network formed by C5 and R6. From C5, the rectified voltage is fed to

logic 0 when the input falls to well under half the supply voltage. This helps to prevent false triggering of the circuit. The latching part of the circuit is based on a D-type bistable, IC3a, which is configured as a T-type (toggle), by tying pin 2 to pin 5. This enables its output Q to latch high when a high-going trigger pulse from IC2b is received at pin 3. It then latches low again when it receives the next pulse. After which the next pulse toggles the output high again, and so on.

TIMING CIRCUIT

The Timing circuit is based around NOR gates IC2c and IC2d, configured as a monostable. The circuit’s time constant (the time that its output stays high once triggered) is set by Fig.1. Block diagram for the Handclap Switch. the value of capacitor C7 and the total resistance through preset VR2 and the Schmitt trigger circuit formed around resistor R9. NOR gates IC2a and IC2b. This circuit The timing formula is T = 0·7 × R × C, “cleans-up’’ the amplitude changes from where T is the time for which the circuit C5 so that well-shaped logic level remains triggered, in seconds, R is the changes are output from IC2b pin 4. resistance in Ohms and C is the capaciThe voltage input to IC2a via R7 has to tance in Farads. rise to well over half of the supply voltThis circuit uses values of R = 1M + age before the output at IC2b will switch 15k = 1015000 ohms, and C = 100mF = to logic 1. The output will only revert to 0·0001F. In theory, therefore, the maximum time the circuit can remain on is: 0·7 × 1015000 × 0·0001 = 71·05 seconds. In practice, component tolerances will produce somewhat different timings, but the formula provides a guide to expectations. If a longer time is required then a larger capacitor can be used, but it should not exceed 2200µF as timings will begin to be unpredictable, due to current leakage through the capacitor. The fixed resistor R9 ensures that the total resistance can never be zero, even if VR2 is set to zero resistance. The value for R9 was chosen so that the minimum timing period is approximately one second. Switch S1 selects whether the latching or timed circuit is used, the chosen output feeding via resistor R10 to transistor TR1. When the output is high, the transistor is turned on, so activating the relay, RLA. Diode D3 prevents back-e.m.f. (voltage spikes) from being generated at the moment that the relay is turned off.

Everyday Practical Electronics, November 2000

POWER SUPPLY

The power supply circuit is also shown in Fig.2. Power is derived from the a.c. mains and transformer T1 provides an isolated output voltage of 9V a.c., at up to about 100mA. A higher-current transformer may be used if preferred. The 9V a.c. supply is bridge-rectified by REC1 and smoothed by capacitor C9, producing a d.c. supply of about 12V. Fuse FS1 is included in the 9V a.c. supply line and should be rated to suit the maximum current that is permitted to be drawn from the transformer. Although not included in the prototype, a fuse should also be included in the mains a.c. live supply line before the connection to the relay and transformer. This should be rated to suit the maximum load that the relay is required to switch, plus about 1A margin for the current through the primary winding of the transformer. A neon lamp, LP1, is wired across the mains supply, following fuse FS2, indicating when mains power is connected.

CONSTRUCTION

Since this unit contains mains voltage, great care should be exercised in its construction. If in any doubt about construction consult a qualified electrician. Mains voltage can be lethal if abused. Apart from the electret microphone, switch, relay and transformer, all the components are contained on a single printed circuit board (p.c.b.). The topside

component layout and the full size underside copper foil track master are shown in Fig.3. This board is available from the EPE PCB Service, code 270. Begin construction by soldering in the resistors and wire links. Ensure that the electrolytic capacitors, transistor, diodes and bridge rectifier are connected the right way round. Use sockets for the three i.c.s, but do not insert the i.c.s until

construction has been completed (ensure their correct orientation when they are fitted). If you choose not to use the timer circuit, VR2, R9, C6 and C7 can be omitted and a wire link inserted to join IC3 pin1 to R10. If you choose to omit the latching circuit, IC3 and C6 can be omitted and a wire link inserted to join IC2d pin11 to R10. In both cases S1 is omitted.

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µ

µ µ

Fig.2. Complete circuit diagram for the Handclap Switch. LP1 NEON

REC1 W005

Everyday Practical Electronics, November 2000

µ

865

COMPONENTS Resistors

See

R1, R7 10k (2 off) R2, R3, 100k R6 (3 off) R4, R8 470k (2 off) page R5 1k R9 15k R10 4k7 All 0·25W 5% carbon film.

SHOP TALK

Potentiometers VR1 VR2

10k min. preset, vertical mounting 1M min. preset, vertical mounting

Capacitors C1 220n ceramic disc C2 to C4 10mF elect. radial, 25V (3 off) C5 1m elect. radial 25V C6, C8 100n ceramic disc (2 off) C7 100m elect. radial, 25V C9 2200m elect. radial, 25V

Semiconductors D1, D2 D3 TR1 REC1 IC1 IC2 IC3

1N4148 signal diode (2 off) 1N4001 rectifier diode BC184L, or other gen. purpose npn transistor W005 50V 1A bridge rectifier 741 op.amp 4001B quad 2-input NOR gate 4013B dual bistable (flip-flop)

Miscellaneous LP1 MIC1 RLA S1 T1 FS1 FS2

Fig.3. Printed circuit board component layout and full size copper foil track master pattern.

CASING The mains voltage section of this unit should be kept in a separate compartment of the box to ensure that it is completely isolated from the low voltage circuit. This is done by inserting a plastic partition inside the case. A small slot should be made at the bottom of it, allowing the low voltage wires from the relay and transformer to come through. The partition should be cut so that it fits securely in the slots provided in the side of the case. The transformer should be firmly bolted to this partition. The relay is glued to it, using good quality adhesive that is suited to the plastic of the partition and of the relay’s cover. It is essential that the relay can never break its bond with the partition. Drill holes in side of the case to suit the positions of the electret microphone, switch S1, mains input cable grommet, neon and fuse FS2. In the lid, drill a hole for fuse FS1

866

and make a cut-out into which the 13A output socket will fit snugly, drilling holes for its mounting bolts as well. Additionally, two holes are required to allow adjustment access to the two preset potentiometers using a small screwdriver. The mains input cable used in the prototype is rated at 3A, which is fine for a low current item such as a desk lamp, for example. However, if you wish to switch higher current appliances, like an electric fire, then mains cable rated at 13A must be used. (The relay must be capable of switching the voltage and current of the appliance to be controlled, i.e. 230V a.c. 13A.) A clamping grommet must be used with the mains input cable to prevent it being pulled out. A set of three terminal blocks is used to connect up the mains to the wires for the transformer, relay and neon. This should be bolted securely to the base of the case, through holes drilled in a suitable position. The mains wires connecting between the

mains neon, panel mounting electret microphone insert min. 12V s.p.s.t. relay, contact rating to suit powered appliance s.p.d.t. toggle switch mains transformer, 9V a.c. 100mA secondary 100mA fuse, 20mm mains rated fuse, value to suit powered appliance (see text)

Printed circuit board, available from the EPE PCB service, code 270; plastic case, 185mm × 115mm × 65mm; plastic insert to suit case (see text); fuseholder, panel mounting, 20mm (2 off); cable grommet, locking, panel mounting; 8-pin d.i.l. socket; 14-pin d.i.l. socket (2 off); 3-way mains rated terminal block, screw terminals, bolt mounting; nuts and bolts to suit; p.c.b. supports, self-adhesive (4 off); mains rated cable (see text); 13A mains socket, flush mounting; earthing solder tag; connecting wire; solder, etc.

Approx. Cost Guidance Only

£23

excluding case and mains socket relay and the output socket must have the same rating as the mains input cable. They are soldered to the relay terminals.

TESTING

Once the p.c.b. has been assembled, fully check for any mistakes, and the quality of soldering.

Everyday Practical Electronics, November 2000

In the prototype, the p.c.b. is secured to the base of the case using self-adhesive p.c.b. supports. However, it is advisable not to fully secure the p.c.b. until testing is complete. The first thing to check is that the d.c. output from the rectifier circuit is the correct voltage, of around 12V. If it is not, immediately disconnect the circuit from the mains and check that the transformer, bridge rectifier and capacitors have been connected correctly. To start testing, adjust preset VR2 for its minimum resistance in series with resistor R9. To adjust preset VR1 to its correct setting, first adjust it for maximum signal output at its wiper, then turn it back about ten degrees. These two settings should give you a sensible level in respect of the amplified electret microphone signal, and also a time delay of one second for the timer circuit.

COMMON PROBLEMS

Typical constructional mistakes include dry solder joints and adjacent p.c.b. track pads accidentally bridged together with solder. Other problems include failure to insert wire links. Also check that the components are correctly placed, and the correct way round.

FAULT FINDING

To assist in fault finding, temporarily disconnect the wires between the p.c.b. and the relay coil. Connect a light emitting diode (l.e.d.), with a 1k9 ballast resistor in

Interior of the assembled Handclap Switch. Note that the mains connections are well isolated from the low voltage circuit and that the central partition fully separates the two sides of the box. This prototype does not include the mains fuse FS2. series, to the p.c.b. terminals provided for the relay coil connection. The l.e.d. will provide you with a way of knowing if the circuit is working. Testing can be done using a multimeter but it is preferable to use an oscilloscope as the signal sometimes fluctuates. Start by again testing the power supply, which should still be around 12V. Next connect the oscilloscope to the positive side of the electret microphone (junction with resistor R1) to see if sounds are being received when you clap hands. After that, check that the voltage at pin 6 of IC1 is at 6V when no sound is occurring, and that the sound signal is amplified when it is present. If a suitably amplified signal is present, check that the voltage at IC2a pins 1 and 2 is above 6V. If this is not so, check that diodes D1, D2 and capacitors C4, C5 are connected the correct way round, and that VR1 is not set to minimum gain. If all is well the output at IC2b pin 4 should be 12V when a sound signal is present. Connect a meter to switch S1 pin 1 then to S1 pin 3. Pin 3 should remain high until you clap your hands again, which should cause it to go low. Pin 1 of switch S1 should remain high for the period set by VR2, R9 and C7 and then go low. If it does not, check that C7 is connected the correct way round.

SETTING UP

Both presets, VR1 and VR2, can be adjusted to suit the user’s particular needs. The following is a summary of their functions: VR1: Sets the sensitivity of the circuit to sound. VR2: Only used if the timer circuit has been selected by switch S1. It sets the time for which the timer remains active. Reducing the resistance reduces the timing period.

IN USE

Fig.4. Interwiring between the two partitioned areas and the off-board components.

Everyday Practical Electronics, November 2000

This design can be used to turn on any normal mains powered domestic appliance, within the limits of the cabling and value of fuse FS2. Plug the appliance into unit’s output socket, clap hands or shout and it will turn on, either: 1) for a timed period up to about 70 seconds, or 2) until you clap or shout again. These options can be chosen with the selection switch S1. $

867

PCB SERVICE Printed circuit boards for most recent EPE constructional projects are available from the PCB Service, see list. These are fabricated in glass fibre, and are fully drilled and roller tinned. All prices include VAT and postage and packing. Add £1 per board for airmail outside of Europe. Remittances should be sent to The PCB Service, Everyday Practical Electronics, Allen House, East Borough, Wimborne, Dorset BH21 1PF. Tel: 01202 881749; Fax 01202 841692; E-mail: [emailprotected]. Cheques should be crossed and made payable to Everyday Practical Electronics (Payment in £ sterling only). NOTE: While 95% of our boards are held in stock and are dispatched within seven days of receipt of order, please allow a maximum of 28 days for delivery – overseas readers allow extra if ordered by surface mail. Back numbers or photostats of articles are available if required – see the Back Issues page for details.

Please check price and availability in the latest issue. Boards can only be supplied on a payment with order basis.

Order Code

PROJECT TITLE oEPE Time Machine Auto-Dim Bedlight Portable 12V PSU/Charger Safe and Sound (Security Bleeper) Surface Thermometer Disco Lights Flasher Waa-Waa Pedal (Multi-project PCB) oVirtual Scope – Digital Board Analogue Board (per board) oWater Wizard Kissometer oEPE PIC Tutorial The Handy Thing (Double-Sided) Lighting-Up Reminder oAudio System Remote Controller – PSU Main Board Simple Metal Detector (Multi-project PCB) oRC-Meter Security Auto-Light Stereo Tone Control plus 20W Stereo Amplifier Tone Control 20W Amplifier oDice Lott EPE Mood Changer (AT89C2051/1051 Programmer Main Board Test Board oReaction Timer Software only oPIC16x84 Toolkit oGreenhouse Computer Control Board PSU Board Float Charger Lightbulb Saver Personal Stereo Amplifier (Multi-project PCB) oGreenhouse Radio Link oPIC Altimeter Voice Processor oDigiserv R/C Expander IR Remote Control – Transmitter – Receiver oPIC Tape Measure Electronic Thermostat – T-Stat PhizzyB A – PCB B – CD-ROM C – Prog. Microcontroller 15-Way IR Remote Control Switch Matrix 15-Way Rec/Decoder Damp Stat Handheld Function Generator oFading Christmas Lights PhizzyB I/O Board (4-section) Twinkle Twinkle Reaction Game oEPE Mind PICkler PhizzyB I/O Board (4-section) Alternative Courtesy Light Controller Light Alarm oWireless Monitoring System Transmitter Receiver oPIC MIDI Sustain Pedal Software only oWireless Monitoring System-2 F.M. Trans/Rec Adaptors oTime and Date Generator Auto Cupboard Light Smoke Absorber Ironing Board Saver Voice Record/Playback Module Mechanical Radio (pair) oVersatile Event Counter PIC Toolkit Mk2 A.M./F.M. Radio Remote Control Transmitter Receiver oMusical Sundial PC Audio Frequency Meter oEPE Mood PICker 12V Battery Tester Intruder Deterrent L.E.D. Stroboscope (Multi-project PCB)

868

Cost

171 172 173 179 174 178 932 176 177 180 181 182 183 184 185 186

£8.34 £6.63 £6.61 £7.32 £7.64 £8.30 £3.00 £14.49 £7.34 £7.69 £7.67 £7.99 £6.58 £5.90 £7.05 £8.29

MAY’98

932 188 189

£3.00 £7.66 £8.10

JUNE’98

190 191 192 193

£7.78 £8.58 £8.05 £7.75

JULY’98

194 195 – 196

£8.50 £8.69 – £6.96

AUG’98 SE SEPT’98

197 198 199 202 932

£9.08 £8.10 £6.59 £3.00 £3.00

NOV’97 DEC’97 JAN ’98 FEB’98

MAR’98

APR’98

SEPT’98 OCT’98

NOV’98

DEC’98

JAN’99

FEB’99

200 201 203 204 205 206 207 208

£8.32 £8.15 £7.18 £7.69 £3.00 £3.50 £6.82 £4.00 £14.95 Bee (A)(B)(C) each 211 212 209 213 215 216 210 214 216 217 218 219+a 220+a – 219a/220a 221 222 223 224 225 226A&B 207 227

£3.00 £4.00 £4.50 £4.00 £5.16 £3.95 £7.55 £6.30 £3.95 £6.72 £6.78 £9.92 £8.56 – See Feb’99 £7.37 £6.36 £5.94 £5.15 £5.12 £7.40 £6.82 £8.95

228 229 231 232 233 234 235 932

£3.00 £3.20 £9.51 £8.79 £6.78 £6.72 £7.10 £3.00

MAR’99

APR’99

MAY’99

JUNE’99 JULY’99

PROJECT TITLE Ultrasonic Puncture Finder o8-Channel Analogue Data Logger Buffer Amplifier (Oscillators Pt 2) Magnetic Field Detective Sound Activated Switch Freezer Alarm (Multi-project PCB) Child Guard Variable Dual Power Supply Micro Power Supply oInterior Lamp Delay Mains Cable Locator (Multi-project PCB) Vibralarm Demister One-Shot oGinormous Stopwatch – Part 1 oGinormous Stopwatch – Part 2 Giant Display Serial Port Converter Loft Guard Scratch Blanker Flashing Snowman (Multi-project PCB) oVideo Cleaner Find It oTeach-In 2000 – Part 4 High Performance Regenerative Receiver oEPE Icebreaker – PCB257, programmed PIC16F877 and floppy disc Parking Warning System oMicro-PICscope Garage Link Transmitter Receiver Versatile Mic/Audio Preamplifier PIR Light Checker oMulti-Channel Transmission System Transmitter Receiver Interface oCanute Tide Predictor oPIC-Gen Frequency Generator/Counter g-Meter oEPE Moodloop Quiz Game Indicator Handy-Amp Active Ferrite Loop Aerial oRemote Control IR Decoder Software only oPIC Dual-Channel Virtual Scope Handclap Switch oPIC Pulsometer Software only

AUG’99

SEPT’99 OCT’99 NOV’99

Order Code 236 237 238 239 240 932 241 242 243 244 932 230 245 246

Cost £5.00 £8.88 £6.96 £6.77 £6.53 £3.00 £7.51 £7.64 £3.50 £7.88 £3.00 £6.93 £6.78 £7.82

247 248 249 250 932 251 252 253 254, 255 256 Set

£7.85 £3.96 £4.44 £4.83 £3.00 £5.63 £4.20 £4.52

DEC’99

JAN’00 FEB’00 MAR’00

APR’00

MAY’00

JUNE’00 JULY’00 AUG’00 SEPT’00 OCT ’00 NOV ’00

}

Set Only 258 259 261 262 260 263

}

264 265 266 267 268 269 271 272 273 274 – 275 270 –

}

£5.49 £22.99 £5.08 £4.99

Set

£5.87 £3.33 £3.17

Set

£6.34 £3.05 £5.07 £4.36 £5.47 £4.52 £4.52 £4.67 – £5.15 £3.96 –

EPE SOFTWARE Software programs for EPE projects marked with an asterisk ( are available on 3.5 inch PC-compatible disks or free from our Internet site. The following disks are available: PIC Tutorial (Mar-May ’98 issues); PIC Toolkit Mk2 (May-Jun ’99 issues); EPE Disk 1 (Apr ’95-Dec ’98 issues); EPE Disk 2 (Jan-Dec ’99); EPE Disk 3 (Jan ’00 issue to current cover date); EPE Teach-In 2000; EPE Interface Disk 1 (October ’00 issue to current cover date). The disks are obtainable from the EPE PCB Service at £3.00 each (UK) to cover our admin costs (the software itself is free). Overseas (each): £3.50 surface mail, £4.95 each airmail. All files can be downloaded free from our Internet FTP site: ftp://ftp.epemag.wimborne.co.uk.

EPE PRINTED CIRCUIT BOARD SERVICE Order Code

Project

Quantity

Price

.............................................................................. Name ................................................................... Address ............................................................... .............................................................................. I enclose payment of £................ (cheque/PO in £ sterling only) to:

Everyday Practical Electronics MasterCard or Visa No. Minimum order for credit cards £5

6666666666666666 Signature....................................... Card Exp. Date................ Please supply name and address of cardholder if different from the address shown

NOTE: You can also order p.c.b.s by phone, Fax, E-mail or via our Internet site on a secure server:

Everyday Practical Electronics, November 2000

KITMASTER EDUCATIONAL KITS RADIO CLUBS – NOVICES – COLLEGES – SCHOOLS SOLID STATE KITS ALL KITS BUILT ON TRIPAD PCB BUILD AS YOU SEE SYSTEM

FULL KIT & INSTRUCTIONS

X1 X3 X5 X7 B2 B4 X11 B44 B8 C1 B61 B9 B10 B11 B12 B13 B14 B15 B16 B17 B18 B19 B20 B21 B22 B23 B24 B25 B26 B27 B28 B29 B30 B31 B32 B33 B34 B35 B36 B37 B38 B39 B40

2-IC MK484 MW RADIO £10.00 1-IC + TRAN MW RADIO £10.00 MK484 + 2030 MW RADIO £18.00 MK484 TUNER MW, NO AMP £6.00 BASIC CRYSTAL SET AMPLIFIED £10.00 WORKSHOP AMPLIFIER £10.00 S. METER £10.50 SIMPLE HF MW ATU £7.50 SW TUNER GENERAL £10.00 BASIC CRYSTAL SET MW £6.50 MW SIGNAL BOOSTER £12.50 FAKE CAR ALARM FLASHER £5.00 2 L.E.D. FLASHER £4.80 LOW VOLTS L.E.D. ALARM 9-12V £5.00 LIE DETECTOR WITH METER £10.00 TOY ORGAN £6.50 METRONOME IC CONTROL £5.00 TOUCH SWITCH £5.00 HEADS OR TAILS GAME £5.00 SIREN £4.80 RAIN DETECTOR £4.80 CONTINUITY TESTER £4.50 MORSE CODE OSCILLATOR £4.80 BURGLAR ALARM L.E.D. & SPEAKER £5.00 LOOP SECURITY ALARM £5.00 VIBRATION ALARM £4.80 METAL DETECTOR + METER £14.00 HAND TREMOR GAME £4.80 RAIN SYNTHESISER – NOISE £10.50 AUTO LIGHT DARK INDICATOR £4.80 ADJ LOW LIGHT INDICATOR £4.80 DARK ACTIVATED L.E.D. FLASHER £4.80 LIGHT ACTIVATED TONE ALARM £4.80 CAR ELECTRIC PROBE £4.50 SIGNAL INJECTOR £4.50 MOISTURE METER – L.E.D. £4.80 L.E.D.TRANSISTOR TESTER NPN £4.50 DIODE TESTER – L.E.D. £4.50 L.E.D. TRANSISTOR TESTER PNP £4.50 IC 555 TESTER – L.E.D. £4.50 0-18 MIN TIMER L.E.D. & SPEAKER £5.50 TOY THERAMIN MUSIC £6.80 AMPLIFIED RF PROBE + METER £10.50

SOLID STATE KITS P&P £3 UK WORLDWIDE P&P £10 PAYMENT CHEQUES STERLING

SOLID STATE KITS

RADIO VALVE KITS

PERFECT FOR NOVICE FIRST TIME BUILDERS IN ELECTRONICS B41 B43 B45 B46 B48 B49 B50 B51 B52 B53 B54 B55 B56 B57 B58 B58A B59 B60 B62 B63 B64 B65 B66 B67 B68 B69 B70 B72 B73 B74 B75 B76 B77 B78 B79 B80 B81 B82 B83 B84 X12 X14 Z1

TRANSMITTER RF INDICATOR L.E.D. £4.80 AUDIO NOISE GENERATOR £10.00 GENERAL 3 TRANSISTOR AMP £5.50 LM386 AMPLIFIER GENERAL £5.50 COMMON PRE-AMP RADIO £5.50 PEST SCARER HIGH PITCH £12.00 VARIABLE FREQ. OSCILLATOR £5.50 AUTOMATIC NIGHT LIGHT £5.50 FROST ALARM £5.80 PRESSURE MAT & ALARM £13.50 GUITAR TUNER £9.50 TOUCH ALARM £5.80 SIMPLE LIGHT METER £13.50 L.E.D. CONTINUITY METER £4.50 SOUND-OPERATED SWITCH £6.50 8 FLASHING L.E.D.s £6.80 TBA 820M AUDIO AMP £10.50 TDA 2030 AUDIO AMP £9.50 ELECTRONIC DICE GAME £8.50 ADVANCED THERAMIN-MUSIC £10.50 TOUCH DELAY LAMP £5.50 FISHERMAN’S ROD BITE ALARM £5.00 BEAM BREAK DETECTOR ALARM £8.00 LATCHING BURGLAR ALARM £7.50 LIGHT-OPERATED RELAY £7.50 MICROPHONE PRE-AMP £7.50 MAGNETIC ALARM-MODELS £7.50 BATH OR WATER BUTT ALARM £6.80 0-18 VOLT POWER SUPPLY UNIT £6.80 FM BUG POWER SUPPLY 0-9V £6.50 1 TRANSISTOR FM BUG £6.50 2 TRANSISTOR FM BUG £7.50 CHIRP GENERATOR £6.80 TONE BURST GENERATOR £6.80 SOUND EFFECTS GENERATOR £10.50 LIGHT METER – PHOTOGRAPHY £10.50 LIGHT OSCILLATOR – PHOTOGRAPHY £9.50 LIGHT-ACTIVATED RELAY £9.50 DARK-ACTIVATED RELAY £9.50 SOUND SIREN + LOUD AMPLIFIER £11.50 AUDIO PROBE £10.50 CHILD SPEAK LAMP £6.50 SW GEN RECEIVER £13.50

SEND FOR FREE CATALOGUE READY BUILT KITS £5 EXTRA

SOLID STATE KITS

K1 K2 K3 K4 K5 K6 K7 K8 K9 K10 K11 K12

K13

K14

K15

VALVE RADIO POWER SUPPLY UNIT IDEAL PSU FOR MOST OF OUR VALVE KITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .£20.00 VALVE RADIO POWER SUPPLY UNIT SIMILAR TO K1 BUT OFFERS HIGHER VOLTAGE OUTPUT ON HT SIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .£22.00 TWO VALVER REGEN RADIO, WORKS ON MW OR SW INTERCHANGEABLE COILS. KITS COMES WITH SPEAKER. GOOD VOLUME . . . . . . . . . . . . . . . . .£25.00 ONE VALVE AMPLIFIER USES THE EL84 VALVE STILL MADE TODAY. IDEAL SHACK AMPLIFIER. GOOD STARTER KIT . . . . . . . . . . . . . . . . . . . . . . . . . . . .£12.00 BATTERY ONE VALVER NOVICE KIT. RUNS ON 36 VOLTS. IDEAL EXPERIMENTAL VALVE PROJECT, ALSO SOLID STATE UNIT INCORPORATED TO GIVE SPEAKER VOLUME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .£15.00 ONE VALVE REGEN RADIO. COMES WITH CRYSTAL EARPIECE. MW, SW . .£15.00 TWO VALVE AMPLIFIER, GOOD VOLUME . . . . . . . . . . . . . . . . . . . . . . . . . . . .£17.50 CRYSTAL SET ONE VALVER, EXPERIMENTAL VALVE + SOLID STATE WITH SPEAKER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .£18.00 ONE VALVER MW RADIO NOT REGEN. SOLID STATE INCORPORATED. GOOD VOLUME WITH SPEAKER SUPPLIED. WORKS VERY WELL . . . . . . . . . . . . . .£22.50 MODERN TWO VALVE RADIO WITH SOLID STATE. THIS RADIO USES TWO VALVES STILL PRODUCED TODAY AND THERE ARE NO COILS TO WIND. IT OPERATES ON MEDIUM WAVE AND HAS NO REGENERATION PROBLEMS .£28.50 TWO VALVE SW GENERAL RECEIVER 6MHz TO 14MHz. USING MODERN SOLID STATE COMBINED WITH VALVE TECHNOLOGY THIS RADIO HAS VERY GOOD VOLUME, BY USING THE ECC83 AND EL84 VALVES . . . . . . . . . . . . . . . . . . .£27.00 TWO VALVE AMPLIFIED CRYSTAL SET RADIO. SIMILAR TO THE K5 PROJECT BUT WITH MORE AMPLIFICATION. THIS IS IDEAL IF YOU ARE INTO EXPERIMENTING WITH CRYSTAL SETS AND YOU REQUIRE LOTS OF VOLUME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .£26.50 TWO VALVER REGEN RADIO MW & SW. THIS REGEN RADIO USES THE EF91 VALVE AS A DETECTOR AND THE ECL80 FOR AUDIO AMPLIFICATION. THE CIRCUITRY IS SIMILAR TO ITS SISTER, THE K3 REGEN RADIO KIT. AS THESE VALVES ARE VERY COMMON THIS KIT IS SLIGHTLY CHEAPER .£24.00 3-VALVE RADIO MW & SW REGEN RADIO WITH RD STAGE ADDED WHICH GIVES MORE SELECTIVITY. ALSO COMES WITH INTERCHANGEABLE COIL FORMER. ALSO RADIO GIVES GOOD VOLUME, EASY TO ASSEMBLE. THIS SET USES TWO EF91 VALVES AND THE ECL80 FOR AUDIO . . . . . . . . . . . . . . . . .£30.00 3-VALVE RADIO MW & SW. ANOTHER DIFFERENT TYPE OF REGENERATION RADIO ALSO WITH ADDED RF STAGE. THIS CIRCUIT USES THE MODERN EL84 VALVE FOR AUDIO COMBINED WITH THE POPULAR EF80 VALVE FOR THE DETECTOR AND THE EF91 FOR THE RF STAGE, THIS MAKES FOR A SUPERIOR REGEN RADIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .£32.00 ALL RADIO CHASSIS PRE-DRILLED AND VALVE BASES FITTED READY FOR QUICK ASSEMBLY

Visit our new web site: http://www.kit-master.co.uk For our catalogue e-mail: [emailprotected] VALVE KITS P&P £6 UK WORLDWIDE P&P £12 PAYMENT CHEQUES STERLING

SOLID STATE KITS

VALVES

CONSTRUCTORS CORNER

VALVES

MAIL ORDER ONLY PLEASE ALLOW UP TO 28 DAYS FOR DELIVERY

VALVES

PROJECTS BY DAVID JOHNS

HOLIDAYS OVER – NOVICES TRY SOME OF THESE SIMPLE SOLID STATE PROJECTS

NIGHTS GETTING DARK EARLY – TIME TO OPEN UP THE SHACK, GET SOME VALVES LIT UP – EASY PROJECTS

Z1

K12

Two-valve Amplified Crystal Set Radio. Similar to the KB project, but with more amplification. This is ideal if you are into experimenting with crystal sets and you require lots of volume to hear those distant stations. Many experiments can be done with this project concerning crystal set aerial designs etc. This kit is a must if you are just starting out into valve building and solid state assembly.

K13

Two-valver Regen Radio MW and SW. This regen radio uses the EF91 valve as a detector and the ECL80 for audio amplification. The circuitry is similar to its sister, the K3 regen radio kit. As these valves are very common, this kit is slightly cheaper. The coil is easy to wind and is interchangeable. The kit comes complete with speaker which has good volume. Many stations can be received. Note: You will need the PSU kit K1 to run this radio.

K14

3-Valve Radio MW and SW. Regen radio with RF stage added which gives more selectivity. Also comes with interchangeable coil former. This radio gives good volume and is easy to assemble. This set uses two EF91 valves and the ECL80 for audio. Good project. Use PSU kit K1 for operation.

X1

X3 X5

B2

SW General Receiver for Novices. This kit is easy to build, ideal experimental project for novices wishing to look into short wave radio. Based on regeneration principles, many stations can be heard at night. It comes with a good amplifier and speaker and runs on 2xPP3 9V batteries. Medium Wave Radio – MK 484IC. This kit is easy to assemble. It gives good results. No outside aerial required. Also gives good volume with speaker, which is included. Runs on 9V and this circuit uses the new MK 484IC with the LM 386. Medium Wave Radio – all transistor. Based on a simple 3-transistor amplifier with a pre-amp. This radio offers good volume, speaker included. The tuner uses the MK 484IC. No outside aerial required. Runs on 9V. MK 484IC + TDA 2030 amp – Medium Wave Radio. This is an excellent medium wave radio using the MK 484IC, with the TDA 2030 amplifier with speaker. It gives up to ten watts power and runs on 18V. If it’s power you want then this is the one. Easy to build and all fits on one p.c.b. This project is recommended and uses only common components. Basic Crystal Set Amplified. First build the crystal set, then a transistor is added which dramatically increases volume. Operates on general SW and MW. This circuit benefits from unusual wave trap aerial which increases sensitivity. Ideal introduction to radio. Many stations can be heard. Crystal earphone supplied.

MAKE POSTAL ORDERS/CHEQUES PAYABLE TO DAVID JOHNS AND SEND TO:

37 GOSBECKS ROAD COLCHESTER, ESSEX CO2 9JR

Everyday Practical Electronics, November 2000

TEL: 07941 252679 FAX: 01206 369226 869

CLASSIFIED

Everyday Practical Electronics reaches twice as many UK readers as any other UK monthly hobby electronics magazine, our audited sales figures prove it. We have been the leading independent monthly magazine in this market for the last fifteen years.

If you want your advertisem*nts to be seen by the largest readership at the most economical price our classified and semi-display pages offer the best value. The prepaid rate for semi-display space is £8 (+VAT) per single column centimetre (minimum 2·5cm). The prepaid rate for classified adverts is 30p (+VAT) per word (minimum 12 words). All cheques, postal orders, etc., to be made payable to Everyday Practical Electronics. VAT must be added. Advertisem*nts, together with remittance, should be sent to Everyday Practical Electronics Advertisem*nts, Mill Lodge, Mill Lane, Thorpe-le-Soken, Essex CO16 0ED. Phone/Fax (01255) 861161. For rates and information on display and classified advertising please contact our Advertisem*nt Manager, Peter Mew as above. Valve Output Transformers: Single ended 50mA, £4.50; push/pull 15W, £27; 30W, £32; 50W, £38; 100W, £53. Mains Transformers: Sec 220V 30mA 6V 1A, £3; 250V 60mA 6V 2A, £5; 250V 80mA 6V 2A, £6. High Voltage Caps: 50mF 350V, 68mF 500V, 150mF 385V, 330mF 400V, 470mF 385V, all £3 ea., 32+32mF 450V £5. Postage extra. Record Decks and Spares: BSR, Garrard, Goldring, motors, arms, wheels, headshells, spindles, etc. Send or phone your want list for quote.

RADIO COMPONENT SPECIALISTS 337 WHITEHORSE ROAD, CROYDON SURREY, CR0 2HS. Tel: (020) 8684 1665 Lots of transformers, high volt caps, valves, output transformers, speakers, in stock. Phone or send your wants list for quote.

Z88

NOW AVAILABLE WITH 128K AND 512K – OZ4

ALSO SPECTRUM AND QL. PARTS W. N. RICHARDSON & CO. PHONE/FAX 01494 8713196 RAVENSMEAD, CHALFONT ST PETER, BUCKS, SL9 0NB

TIS – Midlinbank Farm Ryeland, Strathaven ML10 6RD Manuals on anything electronic Circuits – VCR £8, CTV £6 Service Manuals from £10 Repair Manuals from £5 P&P any order £2.50 Write, or ring 01357 440280 for full details of our lending service and FREE quote for any data

BTEC ELECTRONICS TECHNICIAN TRAINING GNVQ ADVANCED ENGINEERING (ELECTRONIC) – PART-TIME HND ELECTRONICS – FULL-TIME B.Eng FOUNDATION – FULL-TIME Next course commences Monday 29th January 2001 FULL PROSPECTUS FROM

LONDON ELECTRONICS COLLEGE (Dept EPE) 20 PENYWERN ROAD EARLS COURT, LONDON SW5 9SU TEL: (020) 7373 8721

THE BRITISH AMATEUR ELECTRONICS CLUB exists to help electronics enthusiasts by personal contact and through a quarterly Newsletter. For membership details, write to the Secretary: Mr. M. P. Moses, 5 Park View, Cwmaman, Aberdare CF44 6PP Space donated by

Everyday Practical Electronics

870

Miscellaneous PRINTED CIRCUIT BOARDS – QUICK SERVICE. Prototype and production artwork raised from magazines or draft designs at low cost. PCBs designed from schematics. Production assembly, wiring and software programming. For details contact Patrick at Agar Circuits, Unit 5, East Belfast Enterprise Park, 308 Albertbridge Road, Belfast, BT5 4GX. Phone 028 9073 8897, Fax 028 9073 1802, E-mail [emailprotected].

FREE PROTOTYPE PRINTED CIRCUIT BOARDS! Free prototype p.c.b. with quantity orders. Call Patrick on 028 9073 8897 for details. Agar Circuits, Unit 5, East Belfast Enterprise Park, 308 Albertbridge Road, Belfast BT5 4GX.

PROTOTYPE PRINTED CIRCUIT BOARDS one offs and quantities, for details send s.a.e. to B. M. Ansbro, 38 Poynings Drive, Hove, Sussex BN3 8GR, or phone/fax Brighton 883871, Mobile 07949 598309.

VALVE ENTHUSIASTS: Capacitors and other parts in stock. For free advice/lists please ring, Geoff Davies (Radio), Tel. 01788 574774.

J Home Automation X-10J L We put you in controlL Why tolerate when you can automate? An extensive range of 230V X-10 products and starter kits available. Uses proven Power Line Carrier technology, no wires required. Products Catalogue available Online. Worldwide delivery. Philips Pronto Intelligent Remote now available!

Laser Business Systems Ltd. E-Mail: [emailprotected] http://www.laser.com Tel: (020) 8441 9788 Fax: (020) 8449 0430

G.C.S.E. ELECTRONIC KITS, at pocket money prices. S.A.E. for FREE catalogue. SIR-KIT Electronics, 52 Severn Road, Clacton, CO15 3RB.

DETECT ATMOSPHERIC ACTIVITY. Unique Designs. Self-addressed envelope: PO Box 694, Saint Helier, JE4 9PZ, Jersey, CI. BUILDING OR PURCHASING AN AUDIO MIXING DESK? Specialists in custom built fully modular mixing desks for hospital radio, talking newspapers for the blind, amateur dramatic groups, local shopping centres, theatres etc. To see and read all about our products visit our pictorial web site at: http:\\www.partridge electronics.co.uk or phone 01268 793256. CLEAROUT: 24 × MC68HC705C8CP plus 11 × M5L8251AP-5 plus Adaptec AHA1520B SCSI-2 card, £130. Clarke, 01509 212002. [emailprotected]. REGULATOR PANELS, 12/35V d.c., adjustable and electronic protection, £4.50. Super amplifier, 30W/25V, £5. K.I.A., 1 Regent Road, Ilkley LS29.

EPE NET ADDRESSES EPE FTP site: ftp://ftp.epemag.wimborne.co.uk Access the FTP site by typing the above into your web browser, or by setting up an FTP session using appropriate FTP software, then go into quoted sub-directories: PIC-project source code files: /pub/PICS PIC projects each have their own folder; navigate to the correct folder and open it, then fetch all the files contained within. Do not try to download the folder itself! EPE text files: /pub/docs Basic Soldering Guide: solder.txt EPE TENS Unit user advice: tens.doc and tens.txt Ingenuity Unlimited submission guidance: ing_unlt.txt New readers and subscribers info: epe_info.txt Newsgroups or Usenet users advice: usenet.txt Ni-Cad discussion: nicadfaq.zip and nicad2.zip Writing for EPE advice: write4us.txt

On-line readers! Try the EPE Chat Zone – a virtually real-time Internet “discussion board” in a simple to use web-based forum!

http://www.epemag.wimborne.co.uk/wwwboard Or buy EPE Online: www.epemag.com

Ensure you set your FTP software to ASCII transfer when fetching text files, or they may be unreadable. Note that any file which ends in .zip needs unzipping before use. Unzip utilities can be downloaded from: http://www.winzip.com or http://www.pkware.com

Everyday Practical Electronics, November 2000

Electrical Contracting & Installation Electrical Engineering C&G/ICS Basic Electronic Engineering C&G/ICS Basic Mechanical Engineering TV and Video Servicing Radio and Hi-Fi Servicing Refrigeration Heating & Air Conditioning Motorcycle Maintenance

FREEPHONE 0500 581 557 Or write to: International Correspondence Schools, FREEPOST 882, 8 Elliot Place, Clydeway Skypark, Glasgow, G3 8BR. Tel: 0500 581 557 or Tel/Fax: Dublin 285 2533.

Please send me my Free Information on your Electronics Courses. Mr/Mrs/Ms/Miss (BLOCK CAPITALS PLEASE)Date of Birth

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From time to time, we permit other carefully screened organisations to write to you about Dept. ZEEE 121000 products and services. If you would prefer not to hear from such organisations please tick box 1

Professional 88-108MHz FM Broadcasting Kits All Our Kits Include Detailed Instructions with Schematics High Quality Screen Printed PCBs High Quality Components Our Product Range Includes

ge

40-pa FRErEca2talogue colou

, Great Speakers value for es, Microphon s, Aerials, ne Headpho s, TV Amps, er Transmitt ets, Leads, ck So s, Plug e Cases, CD Storag rity, cu Se , ors, CCTV ors, Adapt Connect es, Gadgets, ox Switch B ting & Disco Ligh ers, ix Effects, M Turntables, s, Amplifier ’ Leads, Car ns ent, Musicia st Equipm Audio, Te , Computer its Hobby K ccessories, A Leads & pplies, Power Su ansformers, Tr s, er rt Inve rgers, ha Battery C ering, ld So s, Tool ses, Fu Switches, , Cable & Indicators overs, ss Wire, Cro ardware, PA H Speaker a great deal d an , ps m A all for the more . . . stamp. a of e ic pr

Transmitters from 0·05W to 35W FM Stereo Coders Audio Compressor Limiters Antennas RF Power Amps Our Kits Are Also Available Fully Assembled And Tested 1W Professional PLL FM Transmitter for Licenced Use in the UK

WE DELIVER WORLD-WIDE AND ACCEPT MAJOR CREDIT CARDS

Visit our Website at http://www.veronica.co.uk

40-42 Cricklewood Broadway London NW2 3ET Tel: 020 8450 0995 Fax: 020 8208 1441 www.skyelectronics.co.uk

Contact Us Now For A Free Brochure Tel 01274 883434

Fax 01274 428665

email [emailprotected]

The Catalogue is FREE to callers or send stamps to the value of £1.85 to cover postage.

Unit 5/6 1A Sandbeds/Albert Rd Queensbury BRADFORD BD13 1AA

2001 CATALOGUE NOW AVAILABLE, FREE OF CHARGE, PLEASE SEND SAE. KITS AVAILABLE FOR MOST EPE PROJECTS. PLEASE SEND SAE FOR DETAILS OF ANY KIT THAT INTERESTS YOU. SPECIAL £1 OFFER PACKS IN OUR 2001 CATALOGUE NOW INCLUDE: 100 50 50 6 4 4 2 3 2 30 4 3

1N4148 SILICON SIGNAL DIODE 1N914 SILICON SIGNAL DIODE 1N4007 1A 1000V RECTIFIER DIODE W005 1·5A 50V BRIDGE RECTIFIER W08 1·5A 800V BRIDGE RECTIFIER 1A 200V SQUARE BRIDGE RECTIFIER 2A 100V SQUARE BRIDGE RECTIFIER 3A 40V IN-LINE BRIDGE RECTIFIER 4A 400V IN-LINE BRIDGE RECTIFIER BC212L TRANSISTOR C108B1 4A 200V THYRISTOR C108D1 4A 400V THYRISTOR

Sky Electronics

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ELECTRONICS 2001

TRAIN TODAY FOR A BETTER FUTURE Now you can get the skills and qualifications you need for career success with an ICS Home Study Course. Learn in the comfort of your own home at the pace and times that suit you. ICS is the world's largest, most experienced home study school. Over the past 100 years ICS have helped nearly 10 million people to improve their job prospects. Find out how we can help YOU. Post or phone today for FREE INFORMATION on the course of your choice

741 OPERATIONAL AMPLIFIER 555 TIMER 4011B CMOS LOGIC 74LS02 SCHOTTKY LOGIC 12V RELAY 430R COIL DPDT 1A CONTACTS ASSORTED ZENER DIODES ASSORTED L.E.D.s ASSORTED TRANSISTORS ASSORTED ½W RESISTORS ASSORTED CAPACITORS CER/FILM/ELECT ASSORTED ELECTROLYTICS ASSORTED FILM CAPACITORS UP TO 2·2mF

PRICE INCLUDES VAT. CLAIM YOUR FREE GIFT WITH ALL ORDERS OVER £10 IN VALUE WITH THIS ADVERT. MAJOR CREDIT CARDS, CHEQUES AND PO’S ACCEPTED. MAIL ORDER ONLY. UK MAINLAND P&P ONLY £1 (EXPORT AT COST MIN. £2).

FML ELECTRONICS

FREEPOST NEA 3627, BEDALE, NORTH YORKSHIRE DL8 2BR

TEL: 01677 425840

ELECTRONICS SURPLUS CLEARANCE SALE SCOOP PURCHASE: FLUKE HAND HELD DIGITAL MULTIMETER, MODEL 8024B Cancelled export order 750V AC/DC 2 amp AC/DC Resistance 20Megohm plus Siemens range. Also measures temperature –20°C to +1265°C. Temp. probe not included. Calibrated for K-type thermocouple. Peak hold facility. Supplied brand new and boxed but with original purchasing organisation’s small identifying mark on case. Test leads and handbook included. Offered at a fraction of original price: £47.50, p&p £6.50 THE ELECTRONICS SURPLUS TRADER – This is a listing of new first class components, books and electronic items at below trade prices. Includes manufacturers’ surplus and overstocks. Also obsolete semiconductors, valves and high voltage caps and components. Send two first class stamps for large catalogue.

(Dept E) CHEVET SUPPLIES LTD

VARIABLE VOLTAGE TRANSFORMERS INPUT 220V/240V AC 50/60Hz OUTPUT 0V-260V PANEL MOUNTING Price P&P 0·5KVA 2·5 amp max £33.00 £6.00 (£45.84 inc VAT) 1KVA 5 amp max £45.25 £7.00 (£61.39 inc VAT) SHROUDED 0·5KVA 2·5 amp max £34.00 £6.00 (£47.00 inc VAT) 1KVA 5 amp max £46.25 £7.00 (£62.57 inc VAT) 2KVA 10 amp max £65.00 £8.50 (£86.36 inc VAT) 3KVA 15 amp max £86.50 £8.50 (£111.63 inc VAT) 5KVA 25 amp max £150.00 (+ Carriage & VAT) Buy direct from the Importers. Keenest prices in the country. 500VA ISOLATION TRANSFORMER Input lead 240V AC. Output via 3-pin 13A socket. 240V AC continuously rated. mounted in fibreglass case with handle. Internally fused.Price £35.00 carriage paid + VAT (£41.13) TOROIDAL L.T. TRANSFORMER Primary 0-240V AC. Secondary 0-30V + 0-30V 600VA. Fixing bolt supplied. Price £25.00 carriage paid + VAT (£29.38) COMPREHENSIVE RANGE OF TRANSFORMERS– LT– ISOLATION & AUTO 110V-240V Auto transfer either cased with American socket and mains lead or open frame type. Available for immediate delivery. ULTRA VIOLET BLACK LIGHT BLUE FLUORESCENT TUBES 4ft. 40 watt £14.00 (callers only) (£16.45 inc VAT) 2ft 20 watt £9.00 (callers only) (£10.58 inc VAT) 12in 8 watt £4.80 + 75p p&p (£6.52 inc VAT) 9in 6 watt £3.96 + 50p p&p (£5.24 inc VAT) 6in 4 watt £3.96 + 50p p&p (£5.24 inc VAT) 230V AC BALLAST KIT For either 6in, 9in or 12in tubes £6.05+£1.40 p&p (£8.75 inc VAT) The above Tubes are 3500/4000 angst. (350-400um) ideal for detecting security markings, effects lighting & Chemical applications. Other Wavelengths of UV TUBE available for Germicidal & Photo Sensitive applications. Please telephone your enquiries. 400 WATT BLACK LIGHT BLUE UV LAMP GES Mercury Vapour lamp suitable for use with a 400W P.F. Ballast. Only £39.95 incl. p&p & VAT

Tel: (01253) 751858. Fax: (01253) 302979

Everyday Practical Electronics, November 2000

16 RPM REVERSIBLE Croucet 220V/230V 50Hz geared motor with ovoid geared box. 4mm dia. shaft. New manuf. surplus. Sold complete with reversing capacitor, connecting block and circ. Overall size: h 68mm x w 52mm x 43mm deep PRICE incl. P&P & VAT £9.99 EPROM ERASURE KIT Build your own EPROM ERASURE for a fraction ot the price of a made-up unit. Kit of parts less case includes 12in. 8watt 2537, Angst Tube Ballast unit, pair of bi-pin leads, neon indicator, on/off switch, safety microswitch and circuit £15.00+£2.00 p&p. (£19.98 inc VAT) WASHING MACHINE WATER PUMP Brand new 240V AC fan cooled. Can be used for a 1 variety of purposes. Inlet 1 /2in., outlet 1in. dia. Price includes p&p & VAT. £11.20 each or 2 for £20.50 inclusive.

SERVICE TRADING CO

157 Dickson Road, BLACKPOOL FY1 2EU E-mail: [emailprotected] Telephone Orders Accepted Callers welcome Tues, Thurs, Fri and Sat.

5 KVA ISOLATION TRANSFORMER As New. Ex-Equipment, fully shrouded, Line Noise Suppression, Ultra Isolation Transformer with terminal covers and knock-out cable entries.Primary 120V/240V, Secondary 120V/240V, 50/60Hz, 0·005pF Capacitance. Size, L 37cm x W 19cmc x H 16cm, Weight 42 kilos. Price £120 + VAT. Ex-warehouse. Carriage on request. 24V DC SIEMENS CONTACTOR Type 3TH8022-0B 2 x NO and 2 x NC 230V AC 10A. Contacts. Screw or Din Rail fixing. Size H 120mm x W 45mm x D 75mm. Brand New Price £7.63 incl. p&p and VAT. 240V AC WESTOOL SOLENOIDS Model TT2 Max. stroke 16mm, 5lb. pull. Base mounting. Rating 1. Model TT6 Max. stroke 25mm, 15lb. pull. Base mounting. Rating 1. Series 400 Max. stroke 28mm, 15lb. pull. Front mounting. Rating 2. Prices inc. p&p & VAT: TT2 £5.88, TT6 £8.81, Series 400 £8.64. AXIAL COOLING FAN 230V AC 120mm square x 38mm 3 blade 10 watt Low Noise fan. Price £7.29 incl. p&p and VAT. Other voltages and sizes available from stock. Please telephone your enquiries. INSTRUMENT CASE Brand new. Manufactured by Imhof. L 31cm x H 18cm x 19cm Deep. Removable front and rear panel for easy assembly of your components. Grey textured finish, complete with case feet. Price £16.45 incl. p&p and VAT. 2 off £28.20 inclusive. DIECAST ALUMINIUM BOX with internal PCB guides. Internal size 265mm x 165mm x 50mm deep. Price £9.93 incl. p&p & VAT. 2 off £17.80 incl. 230V AC SYNCHRONOUS GEARED MOTORS Brand new Ovoid Gearbox Crouzet type motors. H 65mm x W 55mm x D 35mm, 4mm dia. shaft x 10mm long. 6 RPM anti cw. £9.99 incl. p&p & VAT. 20 RPM anti cw. Depth 40mm. £11.16 incl. p&p & VAT.

Open Monday/Friday

57 BRIDGMAN ROAD, CHISWICK, LONDON W4 5BB Tel: 0181-995 1560 FAX: 0181-995 0549

Ample Parking Space

871

Millions of quality components at lowest ever prices!

Watch Slides on TV. Make videos of your slides. Digitise your slides (using a video capture card) “Liesgang diatv” automatic slide viewer with built in high quality colour TV camera. It has a composite video output to a phono plug (SCART & BNC adaptors are available). They are in very good condition with few signs of use. £91.91 + VAT = £108.00 Board cameras all with 512 x 582 pixels 8·5mm 1/3 inch sensor and composite video out. All need to be housed in your own enclosure and have fragile exposed surface mount parts. They all require a power supply of between 10V and 12V DC 150mA. 47MIR size 60 x 36 x 27mm with 6 infra red LEDs (gives the same illumination as a small torch but is not visible to the human eye) £37.00 + VAT = £43.48 30MP size 32 x 32 x 14mm spy camera with a fixed focus pin hole lens for hiding behind a very small hole £35.00 + VAT = £41.13 40MC size 39 x 38 x 27mm camera for ‘C’ mount lens these give a much sharper image than with the smaller lenses £32.00 + VAT = £37.60 Economy C mount lenses all fixed focus & fixed iris VSL1220F 12mm F1.6 12 x 15 degrees viewing angle £15.97 + VAT £18.76 VSL4022F 4mm F1·22 63 x 47 degrees viewing angle £17.65 + VAT £20.74 VSL6022F 6mm F1·22 42 x 32 degrees viewing angle £19.05 + VAT £22.38 VSL8020F 8mm F1·22 32 x 24 degrees viewing angle £19.90 + VAT £23.38 VSL1614F 16mm F1·6 30 x 24 degrees viewing angle £26.43 + VAT £31.06 VWL813M 8mm F1.3 with iris 56 x 42 degrees viewing angle £77.45 + VAT = £91.00 1206 surface mount resistors E12 values 10 ohm to 1M ohm 100 of 1 value £1.00 + VAT 1000 of 1 value £5.00 + VAT 866 battery pack originally intended to be used with an orbitel mobile telephone it contains 10 1·6Ah sub C batteries (42 x 22 dia. the size usually used in cordless screwdrivers etc.) the pack is new and unused and can be broken open quite easily £7.46 + VAT = £8.77 Please add £1.66 + vat = £1.95 postage & packing per order

JPG Electronics 276-278 Chatsworth Road, Chesterfield, S40 2BH. Tel 01246 211202 Fax 01246 550959 Mastercard/Visa/Switch Callers welcome 9.30 a.m. to 5.30 p.m. Monday to Saturday

SHERWOOD ELECTRONICS Buy 10 x £1 Special Packs and choose another one FREE 15 x 5mm Red LEDs 12 x 5mm Green LEDs 12 x 5mm Yellow LEDs 15 x 3mm Red LEDs 12 x 3mm Green LEDs 100 x 1N4148 diodes 30 x 1N4001 diodes 30 x 1N4002 diodes 20 x BC182 transistors 20 x BC184 transistors 20 x BC212 transistors 20 x BC549 transistors 4 x CMOS 4001 4 x 555 timers 4 x 741 Op.Amps 4 x CMOS 4011 3 x CMOS 4013 4 x CMOS 4071 20 x 1N914 diodes 25 x 10/25V radial elect. caps. 15 x 100/35V radial elect. caps. 10 x 470/16V radial elect. caps. 15 x BC237 transistors 20 x Mixed transistors 200 x Mixed 0·25W C.F. resistors 5 x Min. PB switches 20 x 8-pin DIL sockets 15 x 14-pin DIL sockets 15 x 16-pin DIL sockets 4 x 74LS00 15 x BC557 transistors 4 x CMOS 4093 5 x ZTX500 transistors 3 x 10mm Red LEDs 3 x 10mm Green LEDs 2 x CMOS 4047 3 x 74LS93 20 x Assorted ceramic disc caps 100 x Mixed 0·5W C.F. resistors

RESISTOR PACKS – C.Film RP3 RP7 RP10 RP4 RP8 RP11

5 each value – total 365 0·25W 10 each value – total 730 0·25W 1000 popular values 0·25W 5 each value-total 365 0·5W 10 each value-total 730 0·5W 1000 popular values 0·5W

£2.85 £4.10 £5.85 £3.80 £6.45 £8.15

SP131 SP133 SP134 SP135 SP136 SP137 SP138 SP140 SP142 SP143 SP145 SP146 SP147 SP151 SP152 SP153 SP154 SP156 SP160 SP161 SP165 SP167 SP168 SP175 SP177 SP182 SP183 SP187 SP191 SP192 SP193 SP194 SP195 SP197 SP198

6 Queensmead Avenue, East Ewell, Epsom, Surrey KT17 3EQ Tel: 07775 945386 or 0208 393 9055 Mail Order UK only. Lists are updated and only 40 are sent out every 2 weeks. This normally ensures that orders can be fulfilled where only a few thousands of an item is available. (Payment is returned if sold out. I do not deal in credit notes).

COVERT VIDEO CAMERAS

Better quality C Mount lenses

SP1 SP2 SP3 SP6 SP7 SP10 SP11 SP12 SP18 SP20 SP21 SP23 SP24 SP25 SP26 SP28 SP29 SP31 SP34 SP36 SP37 SP39 SP40 SP41 SP42 SP47 SP102 SP103 SP104 SP105 SP109 SP112 SP114 SP115 SP116 SP118 SP120 SP124 SP130

Plus anything from bankruptcy – theft recovery – frustrated orders – over productions etc. Send 54p stamped self-addressed label or envelope for clearance lists. Brian J Reed

2 x TL071 Op.Amps 20 x 1N4004 diodes 15 x 1N4007 diodes 6 x Min. slide switches 3 x BFY50 transistors 4 x W005 1·5A bridge rectifiers 20 x 2·2/63V radial elect. caps. 3 x W04 1·5A bridge rectifiers 2 x CMOS 4017 5 Pairs min. crocodile clips (Red & Black) 6 x ZTX300 transistors 10 x 2N3704 transistors 5 x Stripboard 9 strips x 25 holes 4 x 8mm Red LEDs 4 x 8mm Green LEDs 4 x 8mm Yellow LEDs 15 x BC548 transistors 3 x Stripboard, 14 strips x 27 holes 10 x 2N3904 transistors 10 x 2N3906 transistors 2 x LF351 Op.Amps 6 x BC107 transistors 6 x BC108 transistors 20 x 1/63V radial elect. caps. 10 x 1A 20mm quick blow fuses 20 x 4·7/63V radial elect. caps. 20 x BC547 transistors 15 x BC239 transistors 3 x CMOS 4023 3 x CMOS 4066 20 x BC213 transistors 8 x OA90 diodes 3 x 10mm Yellow LEDs 6 x 20 pin DIL sockets 5 x 24 pin DIL sockets

2 0 0 0 Catalogue now available £1 inc. P&P or FREE with first order. P&P £1.25 per order. NO VAT Orders to: Sherwood Electronics, 7 Williamson St., Mansfield, Notts. NG19 6TD.

Black and White Pin Hole Board Cameras with Audio. Cameras in P.I.R., Radios, Clocks, Briefcases etc. Transmitting Cameras with Receiver (Wireless). Cameras as above with colour. Audio Surveillance Kits and Ready Built Units, Bug Detector etc.

A.L. ELECTRONICS Please phone 0181 203 6008 for free catalogue. Fax 0181 201 5359 E-mail: [emailprotected] www.uspy.com New DTI approved Video Transmitters and Receivers (Wireless) Major credit cards now taken

ADVERTISERS INDEX A.L. ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .872 N. R. BARDWELL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .860 BELL COLLEGE OF TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . .854 B.K. ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Cover (iii)/840 BRIAN J. REED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .872 BRUNNING SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .827 BULL ELECTRICAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Cover (ii) CHEVET SUPPLIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .871 CRICKLEWOOD ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .818 CROWNHILL ASSOCIATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .837 DAVID JOHNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .869 DISPLAY ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794 ECONOMATICS (EDUCATION) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .839 EPTSOFT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Cover (iv) ESR ELECTRONIC COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .802 FML ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .871 FOREST ELECTRONIC DEVELOPMENTS . . . . . . . . . . . . . . . . . . . . . . . 819 GREENWELD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .818 ICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .871 J&N FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .798 JPG ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .872 LABCENTER ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .809 MAGENTA ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .800/801/808 MAPLIN ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .849 MICROCHIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .813 MILFORD INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .825 NATIONAL COLLEGE OF TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . .824 PEAK ELECTRONIC DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .816 PICO TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .797 QUASAR ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .796 REVOLUTION EDUCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .840 SERVICE TRADING CO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871 SHERWOOD ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .872 SKY ELECTRONICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .871 SLM (MODEL) ENGINEERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .854 SQUIRES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .824 STEWART OF READING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .848 SUMA DESIGNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .855 TELNET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799 VERONICA KITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .871

ADVERTIsem*nT MANAGER: PETER J. MEW ADVERTIsem*nT OFFICES: EVERYDAY PRACTICAL ELECTRONICS, ADVERTIsem*nTS, MILL LODGE, MILL LANE, THORPE-LE-SOKEN, ESSEX CO16 0ED. Phone/Fax: (01255) 861161

For Editorial address and phone numbers see page 803

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