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By JOHN CLARKE Build a one or two-lamp flasher This simple circuit lets you flash one halogen lamp at about twice a second to simulate a low frequency strobe or you can flash a pair of halogen lights alternately at rates from once a second to once every three seconds or so. You can use the flasher circuit to draw attention to a sign or wall display or simply just to liven up the atmosphere at a party. 64  Silicon Chip Flashing lights are a good way of attracting peoples’ attention. They are used to good effect on many advertising displays and at shows, particularly car & boat stands where the very latest high tech items are to be seen. Flashing lights are also often used at parties and the best example of this is the Light Show presented elsewhere in this issue. If your budget doesn’t run to a full-blown light show this project could give you at least some of the visual effect. The circuit is quite simple and provides for two varia­ tions. In its simplest strobe form it uses just one 555 timer IC and one Mosfet. In its two-lamp form it uses the 555, a 4013 time to cool and the effect would be merely a flicker in the lamp bright­ ness rather than flashing on and off. Hence the strobe effect is not like that from an Xenon flash tube which can be driven at very fast rates to give the effect of stopped or jerky motion of moving objects. Circuit description Fig.1 shows the strobe version of the circuit, IC1 is a standard 555 timer which is connected to operate as an astable oscillator. Initially, when power is first applied, the 47µF capacitor at pins 2 and 6 is discharged and pin 3 is high. It is charged via diode D2 and the 10kΩ connecting to the positive supply. When the capacitor voltage reaches 2/3rds Fig.1: the single lamp version of the circuit uses a 555 timer to drive a Mosfet which the supply, as detected by pin 6, flashes the lamp. Diode D2 ensures that the flash duration is fixed at about half a pin 7 goes low to discharge the second while the flash repetition rate is varied by VR1. 47µF capacitor via potentiometer VR1 and the series 10kΩ resistor. flipflop IC and two Mosfets. It can run At the same time as pin 7 goes low, Main Features from 12V DC or 12V AC. so does pin 3. The strobe version simply flashes When the 47µF capacitor is disone lamp on and off with a fixed lamp charged to 1/3rd the supply voltage, •  Strobe (one lamp) or flasher (two lamp) operation on time of about 0.5s and a variable off as detected at pin 2, pin 7 goes open duration from 0.5s to about 3.5s. The circuit and pin 3 goes high again. •  Adjustable flash rate flasher version switches each lamp Thus the capacitor charges again. on at between 1s and 4s as set by the Its voltage swings between 1/3rd and •  Operates from 12VAC or 2/ rds the supply while the voltage variable rate control. The flash rate 3 12VDC supply is limited in practical terms by the at pin 3 switches high and low at the thermal inertia of the halogen lamp’s same rate. •  Drives 20W or 50W halogen filament. If we were to flash the lamp Diode D2 is included between pin 7 lights too fast the filament would not have and 2 & 6 so that the capacitor charge Fig.2: the two-lamp version of the circuit adds a flipflop and another Mosfet to drive the second lamp. The flipflop is used to ensure that each lamp is on for precisely half the time. January 1998  65 Fig.3: component layout for the single lamp version. Note that one IC and one Mosfet position is vacant. rate is fixed and not dependent on the adjust­ment of VR1. This makes the duration of each flash constant while the time interval between flashes is adjustable. The pulse waveform at pin 3 of IC1 drives the gate of Mosfet Q1 via a 10Ω resistor. The Mosfet then drives the halogen lamp. Flasher circuit Fig.2 shows the flasher version of the circuit. Instead of driving a Mosfet, pin 3 of IC1 drives one half of a 4013 dual D-type flipflop. So each time pin 3 of IC1 goes high, it causes the Q and Q-bar outputs of IC2 to change state; ie, change from low to high or from high to low. The Q and Q-bar outputs of the flipflop then drive the gates of Mosfets Q1 and Q2 via 10Ω resistors. Each Mosfet then drives its own halogen lamp. So far, so good but some readers will ask why we bothered to use the flipflop in order to drive two Mosfets for alternately flashing the lamps. Why not just drive the second Mosfet from the drain of the first Mosfet? That would work but it wouldn’t look good, particularly if the flash rate was slow, say, once every three seconds. What you would find is that one lamp would be on for half a second, as set by D2, the 10kΩ resistor and the 47µF timing Resistor Colour Codes ❏ No. ❏  2 ❏  1 ❏  1 ❏  1 66  Silicon Chip Value 10kΩ 2.2kΩ 22Ω 10Ω 4-Band Code (1%) brown black orange brown red red red brown red red black brown brown black black brown 5-Band Code (1%) brown black black red brown red red black brown brown red red black gold brown brown black black gold brown Fig.4: component layout for the twolamp version. Note that a heatsink must be fitted to the bridge rectifier if 50W lamps are used. capacitor. But the other lamp would then be on for three seconds before the circuit flicked back to the first lamp. That would mean that one lamp would be on for most of the time and so the display would not look good. With the flipflop in circuit each lamp would be on for precisely the same amount of time, regardless of how the flashing rate potentiometer was set. DC or AC Both Fig.1 and Fig.2 show the supply input to the circuit via a bridge rectifier and that means that the circuit can run on 12V DC or 12V AC. A secondary benefit of the bridge rectifier is that if you are using a 12V DC battery or power supply, you can’t accidentally damage the circuit by connecting the supply the wrong way around. When you are using a 12V AC sup- Fig.5: actual size artwork for the PC board. Check the board carefully before installing any of the parts. ply, diode D1 isolates the rectified but unfiltered lamp supply from the supply for the ICs which is filtered by a 100µF capacitor and protected from voltage transients with a 16V zener diode, ZD1. The 0.68µF capacitor across the unfiltered DC supply prev­ents voltJanuary 1998  67 age overshoot when the Mosfets turn off. LED1 indicates when power is switched on via switch S1. Construction To make connecting the lamps easy, use the wired lamp bases. Trying to solder wires to the pins of the lamps is not really satisfactory. Parts List 1 PC board, code 16301981, 105 x 60mm 2 2-way PC mount terminal strips 1 DPDT miniature slider switch (S1) 1 12V 50W or 20W halogen lamp 1 base to suit halogen lamp (Jaycar Sl-2735 or equivalent) 1 mini heatsink, 20 x 20 x 10mm (Altronics H-0630 or equivalent) 1 mini U-shaped heatsink, 28 x 25 x 34mm (Altronics H-0625 or equivalent; for bridge rectifier) 2 3mm screws and nuts 1 100kΩ linear pot (VR1) 1 knob for VR1 1 3AG in-line fuse holder 1 3AG 6A fuse 1 5mm red LED (LED1) 3 PC stakes 1 60mm length of 0.8mm tinned copper wire Semiconductors 1 555 timer (IC1) 1 PW04 10A 400V bridge rectifier (BR1) 1 1N4004 1A 400V diode (D1) 1 1N914, 1N4148 signal diode (D2) 68  Silicon Chip 1 16V 1W zener diode (ZD1) 1 MTP3055E 12A 60V avalanche protected Mosfet (Q1) Capacitors 1 100µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.68µF 250VDC MKT polyester 1 0.1µF MKT polyester Resistors (0.25W, 1%) 2 10kΩ 1 22Ω 1 2.2kΩ 1 10Ω Extra Parts required for flasher circuit 1 12V 50W or 20W halogen lamp 1 base to suit halogen lamp (Jaycar Sl-2735 or equivalent) 1 2-way PC mounting terminal strip 1 mini heatsink, 20 x 20 x 10mm (Altronics H-0630 or equivalent) 1 3mm screw and nut 1 MTP3055E 12A 60V avalanche protected Mosfet (Q2) 1 4013 dual D flipflop (IC2) 1 10Ω 0.25W 1% resistor (R1) Both versions of the circuit can be built on a PC board coded 16301981 and measuring 105 x 60mm. Fig.3 shows the compon­ent layout for the single lamp (strobe) version. Note that the positions for IC2 and Q2 are vacant and there are three links to be inserted. Fig.4 shows the component layout for the two-lamp version and this has both ICs present. Note that we have specified an in-line fuse for both versions. All components apart from the in-line fuse and lamps mount on the PC board. Follow the appropriate component layout diagram to build either the strobe or flasher. Start by installing and soldering in all the resistors using the accompanying colour code table as an aid in finding the values. Then insert and solder the PC stakes located at the three locations for VR1’s terminals. When the ICs are inserted, make sure they are oriented with pin 1 in the position shown. Diodes D1 and D2 and ZD1 mount with their cathode stripes closest to the slide switch S1. Make sure that the three electrolytic capacitors are ori­ented with the polarity shown. S1 is installed by inserting the switch pins into the PC board and soldering in place. If the pins are difficult to insert, crimp them with pliers first or use tinned copper wire through the switch pins which then insert into the PC board. LED1 mounts onto the PC board with the orientation shown. The potentiometer VR1 mounts with the terminals soldered to the tops of three PC stakes. The Mosfets are mounted with small heatsinks bolted to their tabs. Most important, a U-shaped heatsink must be bolted to the bridge rectifier if you are building the two-lamp version with 50W lamps. With two 50W lamps being driven, the bridge rectifier passes over 4A and dissipates over 6W so it is not surprising that it becomes a little red in the face if a heatsink is not fitted. On the other hand, if you are using 20W lamps, the heat­sink should not be necessary. The lamp and power supply con- SUNSHINE DEVICE PROGRAMMERS Power 100 Universal Programmer 48-pin Textool Socket para I/F ............$1371 Hep 101 Value for Money 8MB E(E)PROM - 1 slave socket ...................$283 Hep 808 High Speed 8MB E(E)PROM programmer 1 master 8 slave sockets .. $790 Jet 08 Production Series E(E)PROM Programmer Stand alone or PC (para) .$1590 PEP01 Portable 8MB E(E)PROM series Programmer, Parallel Port ....................$295 EML2M EPROM Emulator ....................$480 Picker 20 Stand Alone IC Dram CMOS Portable Tester ......................................$199 RU20IT 16 Piece UV EPROM Eraser with timer .............................................$187 Plus converters, adapters & eproms. Contact us for other spe­cialised development tools or data acquisition, industrial elec­tronics, computer and electronic parts and service. Available from: D.G.E. Systems; Nucleus Computer; Stewart Electronics; TECS; X-ON. SUNSHINE ELECTRONICS 9b Morton Ave, Carnegie, Vic, 3163 TEL: (03) 9569 1388 FAX: (03) 9569 1540 Email: nucleus<at>ozemail.com.au Floppy Index This photo shows the board assembled for a two-lamp version of the circuit and with the bridge rectifier fitted with a heatsink. This is necessary if 50W lamps are used. nections to the board are made via PC-mounting insulated terminal blocks. These enable connections to be made easily with a small screwdriver. Connect up the lamp or lamps with the wired base connectors to the output terminals and apply power. Note that you will need a 12V battery or a DC power supply which can deliver about 2A for two 20W lamps and 4.2A for two 50W lamps. For AC operation the halogen lamp transformer from Jaycar (Cat MP-3050) would be suitable. This transformer includes a wired in mains lead and plug, making it safe from the mains voltage. If the lamps fail to flash, check your board for faults including shorts between tracks and breaks. Also check that all the components are in their correct place with correct orienta­tion. The DC supply to IC1 and IC2 should be about 11V between pins 1 and 8 of IC1 and pins 14 and 7 for IC2. You can add colour to the flasher by placing a layer of tinted Cellophane over the halogen lamps but it should not touch the lens or lamp reflectors, as they become quite hot. If you want to alter the flash rate from the presently available range with VR1, change the 47µF capacitor to a smaller value for faster rates and to a SC larger value for slower flashes. Now you can search through all the articles ever published in SILICON CHIP. Whether it is a feature article, a project, a circuit notebook item, an article by one of our regular contributors or a major product review, it does not matter; they are all there, for you to browse through. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit IBM compatible computers. Also included is a handy file viewer with a search utility. Price: $7.00 plus $3 p&p. Send your order to SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bank­ card, Visacard and Mastercard). January 1998  69