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1 Copyright 2008, Wimorne Pulishing Ltd (Sequoia House, 398a ingwood oad, Ferndown, Dorset BH22 9AU, UK) and TehBites Interative In., (PO Box 857, Madison, Alaama 35758, USA) All rights reserved. The materials and works ontained within EPE Online whih are made availale y Wimorne Pulishing Ltd and TehBites Interative In are opyrighted. TehBites Interative In and Wimorne Pulishing Ltd have used their est efforts in preparing these materials and works. However, TehBites Interative In and Wimorne Pulishing Ltd make no warranties of any kind, expressed or implied, with regard to the doumentation or data ontained herein, and speifially dislaim, without limitation, any implied warranties of merhantaility and fitness for a partiular purpose. Beause of possile varianes in the quality and ondition of materials and workmanship used y readers, EPE Online, its pulishers and agents dislaim any responsiility for the safe and proper funtioning of reader onstruted projets ased on or from information pulished in these materials and works. In no event shall TehBites Interative In or Wimorne Pulishing Ltd e responsile or liale for any loss of profit or any other ommerial damages, inluding ut not limited to speial, inidental, onsequential, or any other damages in onnetion with or arising out of furnishing, performane, or use of these materials and works. EADES TECHNICAL ENQUIIES We are unale to offer any advie on the use, purhase, repair or modifiation of ommerial equipment or the inorporation or modifiation of designs pulished in the magazine. We regret that we annot provide data or answer queries on artiles or projets that are more than five years old. We are not ale to answer tehnial queries on the phone. POJECTS AND CICUITS All reasonale preautions are taken to ensure that the advie and data given to readers is reliale. We annot, however, guarantee it and we annot aept legal responsiility for it. A numer of projets and iruits pulished in EPE employ voltages that an e lethal. You should not uild, test, modify or renovate any item of mains powered equipment unless you fully understand the safety aspets involved and you use an CD adaptor. COMPONENT SUPPLIES We do not supply eletroni omponents or kits for uilding the projets featured; these an e supplied y advertisers in our puliation Pratial Everyday Eletronis. Our we site is loated at We advise readers to hek that all parts are still availale efore ommening any projet. To order you opy for only $18.95 for 12 issues go to

2 AUTOMATIC NIGHTLIGHT y OBET PENFOLD This latest, low-ost starter projet is sure to e a turnon. Just a gentle tap or lap will trigger it into life. This simple nightlight starter projet is swithed on simply y tapping on the ase, or gently lapping one s hands lose to the unit. The low power ul then swithes on for approximately five minutes, ut it an e swithed off at any time y operating a eset utton on the top of the ase. The unit was primarily designed with hildren in mind, ut it ould oviously e a useful gadget for adults as well, partiularly disaled people. It is attery powered and is therefore safe for use y small hildren. The simple iruit and lak of mains power also makes this projet suitale for onstrution y omplete eginners. SYSTEM OPEATION The lok diagram of Fig.1 helps to explain how the Automati Nightlight funtions. It is ased on a monostale, whih is simply a iruit that MICOPHONE AMPLIFIE provides an output pulse of a ertain duration eah time it is triggered. In this ase we require the light ul to e swithed on for aout five minutes, and the timing omponents in the ESET MONOSTABLE OUTPUT TANSISTO Fig.1. Blok diagram for the Automati Nightlight. monostale are therefore hosen for an output pulse of this duration. The monostale annot provide suffiient urrent to power the ul, whih is therefore ontrolled y way of a single transistor output stage. Also, an input of the monostale permits the output pulse to e terminated prematurely and the LAMP eset swith ontrols this input. A piezoeletri mirophone is used to provide the trigger signal for the monostale, ut the output signal from the miro phone is too low to provide reliale triggering. A single stage amplifier is therefore used to oost the signal from the mirophone to a level that gives etter results. The sensitivity of the iruit is still quite low, ut high sensitivity is not an advantage in this appliation. It would simply result in frequent spurious triggering of the unit, and operating the eset swith would produe virations that would immediately re-trigger the unit. EPE Online, June

3 CICUIT OPEATION The full iruit diagram for the Automati Nightlight projet appears in Fig.2. It is ased on a low power version of the 555 timer (IC1) used in the standard monostale mode. It is important to use a low power 555 in this iruit, eause it will e left swithed on, ut in the standy mode, for long periods of time. The standard 555 has a urrent onsumption of only a few milliamps, ut over a period of several nights this would signifiantly drain the atteries. A low power 555 onsumes only a fration of a milliamp, and should not greatly drain the atteries, even after a few months of use. ON TIME The timing omponents in the monostale are resistor 3 and apaitor C2. Under standy onditions an internal transistor of IC1 plaes a virtual short iruit aross C2 that prevents it from harging via 3. This short iruit is removed when IC1 is triggered, and C2 then harges via 3 until the C1 47µ MIC1 1 10M 2 47k T1 BC549 MICOPHONE e ESET 3 2M7 C2 100µ 4 10k harge potential equals approximately two thirds of the supply potential. The internal transistor then swithes on again, and almost instantly disharges apaitor C2. Under standy onditions the output at pin 3 of IC1 is low, ut it goes high while apaitor C2 is harging. The output pulse duration is equal to approximately 1 1 C seonds, with the apaitane value in mirofarads and the resistane in megohms. 4 8 ST +V 6 THES. 7 2 Construtional Projet Completed iruit oard showing the omponent layout and the use of an IC soket for the low power 555 timer IC. IC1 TS555CN 1 3 OUT 5 2k2 +6V DIS. TIG. LP1 6V 60mA T2 BC337 e S2 ON/0FF Fig.2. Complete iruit diagram for the Automati nightlight. GND 0V LAMP B1 6V With the speified values this works out at 297 seonds, or just under five minutes in other words. In pratie the pulse duration is likely to e somewhat longer than this due to slight leakage in C2, and it is not possile to set highly aurate output pulse times with a simple iruit of this type. In the present appliation highly aurate results are not required, and any slight lak of onsisteny in the output times is also of little importane. Different output times an e produed y hanging the value of resistor 3 and (or) apaitor C2, ut times of more than aout 20 minutes eome inreasingly unreliale due to the high values involved. However, longer times are not really needed in this appliation, and for most purposes the speified values will suffie. LIGHTING UP TIME Although light ul LP1 is a low urrent (60mA) type, it still requires more urrent than IC1 an supply. Consequently, it is driven via ommon emitter swithing transistor T2. When the output of IC1 goes high T2 is iased into ondution, and LP1 is EPE Online, June

4 COMPONENTS esistors 1 10M 2 47k 3 2M7 4 10k 5 2k2 All 0.25W 5% aron film Capaitors C1 47u radial eletrolyti, 16V C2 100u radial eletrolyti, 10V Semiondutors T1 BC549 npn general-purpose transistor T2 BC337 npn medium-power transistor IC1 TS555CN low power timer Misellaneous MIC1 ased piezoeletri sounder LP1 6V 60mA ul, with holder S1 push-utton swith, push-tomake, release-to-reak S2 s.p.s.t. miniature toggle swith B1 6V attery pak (4 x AA ells in holder) Medium size plasti or metal ox, style and size to hoie; 0.1 inh matrix stripoard, 24 holes y 18 opper strips; 8-pin DIL soket; PP3 type attery onnetor; multistrand onneting wire; solder pins, solder, et. See also the SHOP TALK Page! $10 Approx. Cost Guidane Only (Exluding Batts & Case) supplied with virtually the full 6V supply. esistor 5 prevents an exessive ase urrent from flowing into T2. The iruit an handle higher output urrents inidentally, ut do not use a ul having a rating of more than aout 250mA. Of ourse, using a ul having a urrent rating of more than 60mA will signifiantly shorten the attery life. esistor 4 takes the reset input of IC1 (pin 4) high so that the monostale funtions normally. Pressing swith S1 pulls pin 4 low and auses the output pulse to e terminated immediately. Of ourse, pressing S1 has no effet if LP1 is not swithed on. INPUT TIGGE The trigger input at pin 2 of IC1 is driven from the output of a simple ommon emitter amplifier ased on transistor T1. To trigger the monostale this input must e taken elow one third of the supply voltage. The high value of ias resistor 1 ensures that under quiesent onditions the output voltage at the olletor () of T1 is half the supply potential or more. When the mirophone MIC1 piks up a sound the olletor voltage of T1 moves either side of its normal level, and if the signal is strong enough the voltage will riefly go elow one third of the supply potential and trigger IC1. Mirophone MIC1 is atually a piezoeletri sounder and not a proper mirophone. In this appliation audio quality is not a onsideration, and a piezo sounder used in reverse as a rude rystal mirophone gives good results at low ost. It is important that the urrent onsumption of the amplifier is very low so that good attery life is otained. The urrent drawn y transistor T1 is typially aout 60uA, and the quiesent urrent onsumption of the iruit as a whole is approximately 250uA. CONSTUCTION This attery-powered Automati Nightlight, the latest in our speial series of low-ost starter projets, is uilt up on a small piee of stripoard. The topside omponent layout, underside details and interwiring to off-oard omponents is shown in Fig.3. Containing just 24 holes Construtional Projet y 18 strips the oard is not a standard size and a larger oard must e trimmed down to this size using a haksaw or a junior haksaw. The two mounting holes are 3mm diameter and will aept either 6BA or metri M2.5 mounting olts. Most plasti stand-offs do not work well with stripoard and it is etter to use mounting olts plus spaers to keep the underside of the oard lear of the ase. The seven reaks in the opper strips an e made using a speial tool, ut a handheld twist drill it of aout 5mm diameter will do the jo just as well. The iruit oard is now ready for the omponents and link-wires to e added. Most low power versions of the 555 timer are not statisensitive, ut it is still advisale to mount this omponent on the oard via a holder. Be areful to fit oth apaitors with the orret polarity. Capaitor C2 must e a good quality omponent if the unit is to funtion properly. Using a low grade apaitor will either give greatly extended output pulses from the monostale, or one triggered the lamp will simply stay swithed on indefinitely. A tantalum apaitor is ideal, ut a good quality eletrolyti omponent should give good results. The five link-wires are made from 22s.w.g. or 24s.w.g. (aout 0 6mm diameter) tinned opper wire. Fit single-sided solder pins to the oard at the points where onnetions to the swithes, the mirophone, et. will eventually e made. CASE A medium size plasti or metal ox will omfortaly EPE Online, June

5 aommodate all the omponents. It is est to mount eset swith S1 on the top panel where it will e easy to operate. The mirophone an e mounted ehind the front panel, ut a large round utout will then e needed for the ody of the omponent. It is easier to mount it on the front surfae of the panel, and only three small holes are then required. Two of these are for the metri M2 or 8BA mounting olts, whih are not normally S1 supplied with the sounder inidentally. The third hole allows the two flying leads to pass through to the interior of the ase. The sounder an e used as a template when marking the positions of the mounting holes. Piezo sounders usually have one lak lead and one red one, whih is presumaly to indiate their phasing. They are not polarized omponents though, and an e onneted either way round in this ase A B C D E F G H I J K L N O P Q P O N M L K J I H G F E D C B A 2 e T1 4 1 MIC1 C e T2 LP1 3 C2 + Construtional Projet ON/OFF S2 ED BLACK TO B1 LIGHT WOK Fig.3. Stripoard topside omponent layout, details of reaks in the underside opper strips and interwiring to off-oard omponents. +6V Fitting the light ul to the ase in a reasonaly neat fashion is the only awkward aspet of onstrution. The original intention was to mount the ul on the top panel using a hassis mounting ul holder. Some form of transparent plasti over would then have een fixed over the ul and holder. The prolem with this method is in finding a suitale over. The method eventually used was to mount the ul holder eneath the top panel, with spaers holding it 12 7mm (0 5 inhes) eneath the panel. This rings the top of the holder roughly flush with the top panel of the ase. A 9mm diameter hole drilled in the top panel enales the ul to e srewed into the holder. This gives a reasonaly neat looking finished artile, ut it is not very hildproof. If small hildren will have aess to the unit it is essential to make aess to the ul more diffiult. One solution is to go for the modern approah, and simply mount everything inside a transparent ase. Another possiility is to mount the ul on top of the main ase, ut to mount a small transparent ase over it. ememer that although aess to the ul must e diffiult, it must e possile so that the ul an e hanged. The small amount of hard wiring is perfetly straightforward. The ul holder has srew terminals, ut you may prefer to remove the srews and make soldered onnetions to the metal terminal plates. Be areful to onnet the attery lip with the polarity shown in Fig.3. EPE Online, June

6 The two halves of the ase opened out to reveal the general positioning of the iruit oard and the interwiring to the front and top panel mounted omponents. Don t forget to leave plenty of room for the attery. Using spaers to mount the ul holder on the underside of the ase lid, aove a 9mm diameter hole to allow the ul to e srewed in from the outside. TESTING When the ompleted unit is first swithed on it is likely that it will e triggered and the lamp will swith on. Operating push swith S1 should swith the lamp off again, ut avoid making too muh viration when operating S1 or the unit will e triggered again. With the lamp swithed off, try tapping the ase or lapping gently near the mirophone to hek that the unit will trigger properly. If there is any sign of a malfuntion, swith off at one and rehek the entire wiring, et. If all is well, hek that the lamp remains swithed on for approximately the orret period. Due to omponent toleranes and slight leakage in timing apaitor C2 there may e a sustantial error in the time that the lamp is swithed on. Anything in the region of 4 5 to 7 Construtional Projet minutes is aeptale. If the swith-on time is far too long, or the lamp fails to swith off at all, it is likely that the leakage level of apaitor C2 is too high. It must then e replaed with a higher quality omponent. Due to its low standy urrent onsumption the Automati Nightlight an e left swithed on all the time, ut it is advisale to swith it off during the daytime. Otherwise there is a risk of it eing triggered oasionally, ausing the lamp to swith on and run down the atteries unneessarily. Finished Automati Nightlight showing the piezoeletri mirophone and on/off swith mounted on the front panel. The ul should e proteted against reakage. EPE Online, June