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Deter car thieves with this simple FLASHING ALARM LIGHT A simple flashing light may be all that is needed to deter a would-be thief and protect your car from theft or damage. It's easy to build and switches on automatically as soon as you turn off the ignition. By SYD McKITRICK* To be effective, an alarm deterrent light must meet three basic criteria. First, it must be bright so that it can be easily seen during the daytime. Second, it should have a professional appearance, to give the impression that it is part of a working alarm sys- tern. And third, it should come on automatically whenever the ignition is switched off - after all, what good is an alarm flasher that you've forgotten to turn on? This simple alarm flasher meets those three basic design aims. It can This larger-than-life view shows the completed PC board, ready for installation in the plastic bezel. A small doh of silicone sealing compound cushions the lamp from the PC board to reduce stress on the lamp leads due to vibration. 24 SILICON CHIP be easily fitted to any car and flashes a small light globe inside a large red bezel to provide a really effective warning - just like a real car burglar alarm. Although several commercial flasher units are already available, this kit will cost considerably less to build, will look just as good, and will survive almost anything the 12V automotive electrical system can dish up. In other words, you get a product that's just as good for less money. Isn't that what building kits is all about! Description The deterrent light is built on a small PC board which is designed to fit inside a ready-made mounting bezel. There are just three wires to connect and these go to ground, a permanent +12V supply rail (via the fusebox) and a switched +12V supply rail (from the "accessories" output of the ignition switch) . When the ignition switch is "on" the deterrent light will be disabled but as soon as the ignition switch is turned to the "off" position the light will begin flashing automatically. Since no extra switch is required to control the flashing light, you don't need to remember to turn it on or off. Before deciding on the final design, we looked at several different ways to attack this project. In the end, the humble 555 timer IC appealed because of its low cost, simplicity and ability to directly drive a light globe. The rest of the components are there mainly to protect the 555, while a 01 1N4004 You can now afford a sate II ite TV system 1sn r------------.---4rl'-H+-Wf...-0+12V IC1 For many years you have probably looked at satellite TV systems and thought "one day". 555 You can now purchase the following K band system for only 1k ' - - - - - - - -- -------------------QCHASSIS $995. 00 B EOC VIEWED FROM BELOW This is about 1/3 the price of corn parable systems FLASHING ALARM LIGHT Here's what you get: Fig.I: the circuit uses 555 timer ICI to flash the lamp at a I-second rate. QI turns the 555 on or off automatically in response to the ignition switch input, .. A 1.8 metre pressed steel prime focus dish antenna, complete with all the mounting hardware - as well as a self supporting ground stand . while ZDI protects the circuit from high-voltage transients. single transistor provides the automatic on/off function. How it works Fig.1 shows the circuit details. ICl is the 555 timer and is wired as an astable oscillator. However, the circuit configuration is somewhat unconventional in that the lamp is not driven by ICl 's pin 3 output. Instead, it is connected between the positive supply rail (+Vee) and pin 7, which is the open collector output of the internal discharge transistor. The maximum allowable supply voltage for a 555 is 16V and so protection against high voltage transients is provided by a 15Q resistor and zener diode ZDl. The associated lµF capacitor provides a low impedance supply for the 555, thus preventing problems that can otherwise occur each time the 555 switches from one state to another. Diode D1 protectsthe circuit against reverse polarity which could occur accidentally during initial installation, or if the 12V battery is removed and then later reconnected the wrong way around. Without D1, the 555 timer .. One super low noise LNB (low noise block converter) l.4dB or better. PARTS LIST 1 12V 55mA lamp (LP1) 1 red bezel, DSE Cat. ZA-5730 1 PC board, code ZA-1394 1 35mm length of 15mm-dia. heatshrink tubing 3 1-metre lengths of hookup wire (red, white & black) 1 cable tie .. One KU band feedhorn and all the mounting hardware as well as a magnetic signal polariser. .. 30 metres oflow loss coaxial cable with a single pair control line. .. A 99 channel infrared control satellite receiver with adjustable IF and audio bandwidth, polarity, and dual digital readout. The IR control unit has a range of approx. 10 metres. Semiconductors 1 555 timer (IC1) 1 BC548 transistor (01) 1 1N4004 diode (01) 1 15V 1W zener diode (ZD1) Before you receive your system the unit is pre-programmed to the popular AUSSAT transponders via the internal EEPROM memory. This unit is also suitable for C band applications. Capacitors 2 1µF 25V monolithic Resistors (0.25W, 5%) 1 820kQ 1 10kQ 1 1kQ 1 15Q CALL, FAX or WRITE to AV-COMM PTY LTD. PO BOX 386, NORTHBRIDGE NSW 2063 PHONE (02) 949 7417 would still be protected by ZDl which would become forward biased. However, the 15Q resistor would protest strongly by producing a stream of black smoke! Where to buy the kit This project was developed by Dick Smith Electronics and is available from all DSE stores or by mail order from PO Box 321, North Ryde, NSW 2113. You can also order by phone on (02) 888 2105. The kit comes complete (Cat K-4200} and sells for $A9.95 plus $A3.00 p&p or $A6.00 p&p for airmail. Note: copyright of the PC board associated with this project is retained by Dick Smith Electronics. * R & D Department, Dick Smith Electronics. FAX (02) 949 7095 All items are available seperately. Ask about our low noise 'C' band LNB, and other inter esting products. All systems are provided with dish pointing details. ----------- 1 Yes Garry, I Please send me more information I on your K band satellite systems. I I Name ............................... ........ I I I I Address ........................ ........... I I ................................................... I I ........................... P/Code ........ .. I I I •. ~~~~~~~~8 .......................... ~;;;~ ..• ------------NOVEMBER 1991 25 ~i1 r,:,, I LAMPG,,... - -~ 01 15\l r-----• 12V FROM BATTERY ·.zo1 ·=>-=•,.__. -~ - C H A S S I S lOk'------.-jmrrrit SWITCH Fig.2: install the link under ICl first, then carefully install the remaining parts on the PC board as described in the text. The three external leads & the lamp leads are installed on the copper side of the board, as is the lµF capacitor beneath IC1. Ql is mounted face-down on the board, with its top butted against the IC pins. Now let's assume that power has been applied to the circuit and that the ignition switch is turned on. In this situation, Ql is biased on and so the lµF timing capacitor on pins 2 & 6 ofICl is kept discharged. Because pin 2 is below the trigger voltage (1/3Vcc), the 555 timer will be held in the triggered state and the open collector output at pin 7 will be non-conducting. This means that the lamp will be off, since only a few microamps of current can flow through it via the 820kQ resistor and Ql. When the ignition switch is turned off, Ql also turns off since it no longer receives base bias current via the l0kQ resistor. The lµF timing capacitor now charges towards the positive supply rail due to the current passing through the light globe and the series 820kQ timing resistor. When the voltage across the capacitor reaches 2/3Vcc, ICl resets and pin 7 switches low and lights the lamp. The lµF timing capacitor now discharges into pin 7 via the 820kQ resistor until, after about 0.5s, it reaches 1/3Vcc. At this point, ICl triggers again, the discharge transistor on pin 7 turns off, and the lamp goes out. The lµF timing capacitor now charges towards 2/3Vcc again and thus the cycle is repeated indefinitely until the ignition switch is turned on again. Provided the recommended bulb is used, the package dissipation is quite low and the circuit operates reliably in very high ambient temperatures. In fact, one of the prototypes was tested at an ambient temperature of 120°C and, apart from the flash rate ·increasing due to the temperature characteristic of the timing capacitor, the circuit continued to work. Construction Begin construction by taking a close look at the PC board. Some of the copper tracks run quite close together and it is worthwhile checking that none of these are bridged due to incorrect board etching. If in doubt, use your multimeter to ensure that there are no shorts between adjacent tracks on the board. At this stage, you should also check that the board fits inside the bezel. If it doesn't fit, carefully file the edges of the board until it does. A soldering iron with a fine tip is required for tp.e assembly work and it must be clean and freshly tinned. Fig.2 shows the parts layout on the PC board. First, install the wire link, using a short length of pigtail cut from one of the resistors. This link fits under ICl, so it needs to go in first. Next, install the three 1-metre long connecting leads. To do this, remove approximately 5mm of insulation from the ends and insert the wires into their pads from the copper side of the board. Bend them over so that they run parallel to the PC board towards the light globe end, then solder the wires and cut off any excess wire that protrudes through to the component side. The four resistors can now be installed. In each case, you will have to bend the pigtails close to the resistor body so that it fits on the board. The same goes for diode Dl which can now be installed, along with zener diode ZDl. Check that these two components are mounted in the correct locations and that they are correctly oriented. Before soldering in ICl, position the lµF timing capacitor on the underside of the PC board so that its The completed PC board is slid inside the plastic lamp bezel until the cable tie touches the end of the collar. It is then secured to the bezel using heatshrink tubing which also serves to anchor the external leads. RESISTOR COLOUR CODES 0 0 0 0 0 26 No Value 4-Band Code 5-Band Code 1 1 1 1 820kQ 10kQ 1kQ 15Q grey red yellow gold brown black orange gold brown black red gold brown green black gold grey red black orange brown brown black black red brown brown black black brown brown brown green black gold brown SILICON CHIP CV:;L=AM=P==~/::::===:::;PtJC;;;B/;::=:::iCABLE TIE ~ I\ COPPER SIDE CONNECTING WIRES Fig.3: this diagram shows how the lamp, cable tie & external leads are arranged. LAMP I -j -, l-i=..=-:_:-:_::-::_:-r=-=.:-=-=-J=-,:-- \ BEZEL Fig.4: the cable tie acts as a stop when the board is slid into the bezel & ensures' that the lamp is correctly positioned. leads pass through the holes provided for it (between pins 1 & 8 of ICl). Bend it over so that it lies flat against the board (see photo) and cut off any excess pigtails that protrude through to the component side. This done, remove the capacitor, install ICl on the component side of the board and solder pins 2-7. Now re-install the capacitor and solder the two remaining IC pins and the capacitor leads. ".:he transistor is mounted with the flat face of its body against the board and its top butted against pins 1 & 2 of the IC. Its collector and emitter leads are bent close to the body so they fit into their respective holes, while the base lead is bent so that it fits into its hole (beneath the lµF decoupling capacitor). Solder the transistor leads, then install the capacitor and the light globe (see Fig.2). To reduce stress on the light globe leads, place a small dab of silicone sealing compound between the globe and the edge of the PC board. The unit is now ready for testing. Testing To test the unit, just connect a 12V DC supply between to the OV and +12V leads and leave the +12V ignition lead disconnected. The globe should immediately begin flashing at a rate of approximately once per second. If this checks out, connect the +12Vignition switch lead to the +12V supply as well and check that the globe stops flashing. It should immediately start again when the ignition switch lead is disconnected. If the unit doesn't stop flashing when you connect the ignition lead to +12V, check transistor Ql. If you can't get the unit to flash at all, check that ICl, Dl and ZDl are all correctly oriented, and that Ql is not shorted between collector and emitter (try removing it from the board). Also, check that pins 4 & 8 ofICl are at +12V and that there are no shorts on the copper side of the board. Assuming everything checks out, run the three external leads towards the light globe end of the board and install a plastic cable tie as shown in Fig.3. This cable tie should sit in the small gap between the four components at the edge of the board and the body of the lµF decoupling capacitor. The locking end of the cable tie should be positioned on the component side of the board, directly above ZDl's cathode lead. Pull the cable tie tight, then bend the connecting leads back over the cable tie so that they now run away from the light globe (see Fig.3). This done, push the completed board up inside the bezel until the cable tie touches the end of the plastic collar (see Fig.4). Finally, install heatshrink tubing over the exposed PC board and the non-threaded part of the collar. This will hold the PC board in place and, together with the cable tie, serve to anchor the connecting leads. Installation To install the unit, first find a suitable location where the flasher will be visible and where there is adequate space behind the panel to accommodate the length of the bezel (approximately 40mm). After that, it's simply a matter of drilling a 15mm diameter hole to mount the bezel and connecting up the three supply leads. Make sure that the permanent +12V supply comes via the fused side of the fusebox and that all connectrons are secure and covered in insulation. If you don't wish to drill a hole in the dashboard, try mounting the bezel in the cigarette lighter holder. All you have to do is wrap some plastic insulation tape around the collar of the bezel until it is a snug fit and then carefully push it home. In most cars, you should have little difficulty in routing the connecting leads through a gap in the back of the holder. SC A small 3mW 670nM visible laser diode head . Just connect it to a battery via a switch. Produces a well collimated beam. You could pay three times our price for a laser pointer or gun sight that uses a similar head . $199 A complete mains filter employing two inductors and three capacitors fitted in a metal shielded IEC socket. We include a 40 joule varistor with each filter! $8.90 ea. or 10 for $65 INFRA RED NIGHT VIEWER MAINS SWITCHES Stock up on these modern, high quality, plastic panel mounting mains rated switches, at a fraction of their real prices: Large 3A, with green rocker and black bcdy $1.20 ea . or 10 for $7 Large 15A , with black rocker and a black body $1.50 ea . or 10 for $10 Small 4A illuminated type, with a red rocker and black body $1.50 ea. or 10 for $10 Not a complete kit, but just the absolute essentials: A new 6032 IR tube and a ready made power supply. You get the tube, the supply, a circuit and basic instructions. $150 ARGON LASER TUBE A used, but guaranteed Argon laser tube with . It needs forced air cooling , 3V at 25A for the filament, 400V trigger voltage, and 90 to 100V across it, at about BA to run. All this to produce minimum output of 30mW, of BLUE BEAM! For INFRA RED LASER DIODES Brand new 5mW 780nM 820nM IR Laser diodes. Visible in low light. Some data/application circuits provided . A suitable driver circuit and the components for this circuit are included. Excellent for IA sights, data links, high quality audio links, security perimeter protection , laser "bugs", etc. $30 Need a collimating lens and a heatsink to suit? $20 the more serious laser enthusiasts! We should have suggested power supply circuits . $800 VISIBLE LASER DIODE BARGAIN We supply a used and guaranteed 3mW, 670nM visible laser d iode, a heatsink, a coll imator, a simple constant current driver circuit and components to suit. A little effort is required to mount and adjust the co llimator, but look at the price $94 12V OPERATED GAS LASER BARGAIN SOME UNUSUAL COMPONENTS A used but guaranteed Hall Effect !Cs $2 ea or 1mW He-Ne tube, and our reliable 12V UNIVERSAL LASER POWER SUPPLY KIT. The supply and the tube fit into inexpensive 50mm SWV plast ic tubing . One tube and one supply for $99. And if you want to add an extra tube to the bargain, just add an extra $25. Yes, two tubes and one supply for a total of $124! Need mains operation? We 10 for $15 1000 pF 15KV Capac itors S12 ea or 5 for $45 11KV Diodes $1.50 ea or 10 for $10 TV Triplers $12 ea or 5 for $50 15KV EHT Power Supply (used) $45 or 3 for $100 Photo Multiplier Tubes can provide a similar package with the same tubes , and a small professional, fully potted, Broken Silicon Solar Cells. Enough for 6V <at> 1.5W 240V laser power supply. RING . $9 $90 Some of the above items are in LIMITED SUPPLY ANY OR AS MANY ITEMS FROM THIS LIST DELIVERED BY SKYROAD EXPRESS TO YOUR DOOR : $10 OATLEY ELECTRONICS PO BOX 89, OATLEY, NSW 2223 Telephone: (02) 579 4985 Fax: (02) 570 7910 Certified p&p: $6 in Aust. NZ (Airmail) : $10 Melbourne Distributor: Electronics World (03) 723 3860 or (03) 723 3094 NOVEMBER 1991 27