Fullscreen HTML5Med Res (??MB)HTML4

Ever forget to turn your car's headlights on at night? Or have you ever left your headlights on & flattened the battery? This automatic headlight controller eliminates both those problems. Automatic controller for car headlights By WALLY HAMMER & JEFF MONEGAL NY ONE who owns a car knows what it's like to turn the key in the ignition only to be greeted by a horrible clicking noise from under the bonnet. Yep, flat battery. Frustrating, isn't it? You grit your teeth, get out, kick the car, mutter and wish that there was some electronic device that would automatically turn your car's lights on when they are needed and off again when they are no longer required. The project presented here will do just that and more. It senses the ambient light level and automatically A switches the parking lights and the headlights on or off to suit the conditions. It is simply wired in parallel with the existing lighting circuit, which means that you can still switch the lights on manually using the existing switch if necessary. To operate the unit, you simply do nothing. Once installed correctly, the project will make the operation of your car's lights fully automatic. When the ambient light drops below a preset level, the parking lights will come on first, followed two seconds later by the headlights but only if the en- gine is running. If you switch the engine off, the lights will also go off. Similarly, the lights will switch off if the ambient light rises above a certain level. Another feature that has been added is a "temporary on" mode. Provided it is dark, the driver can switch the lights on for about 30 seconds by pressing a switch, after which time they will automatically turn off. This feature is useful for providing light to find your way to the front door, for example. All car batteries should be able to power the lights for over 30 minutes, so 30 seconds won't cause any problems with battery charge. How it works The prototype was built into two plastic jiffy cases, with the larger unit mounted behind the dashboard. The smaller case contains only the indicator LED, the "TEMPORARY ON" switch, and the LDR (on the back panel). 28 SILICON CHIP Refer now to Fig.1 for the circuit details. Schmitt trigger stage ICla and its associated components shape the pulses from the negative side of the coil primary to produce a series of square-wave pulses on pin 2. When the engine is off, pin 1 of ICla is held high py a lO0kn resistor and pin 2 stays low. However, when the engine is running, negative going pulses from the coil pass via Dl to ICla's input, which then switches its output high and low according to the pulse frequency. The resulting square-wave pulses on pin 2 ofICla are differentiated by a .00lµF capacitor and then inverted by IC1b to produce a train of short positive going pulses at pin 12. These pulses are detected by D5 and used to charge a lµF capacitor. If the engine is running, there will be enough pulses (even at idle) to charge the 1µF capacitor sufficiently to produce a logic high on pin 1 of ICZa. However, if the engine is stopped or is only being cranked over with the starter motor, then the pulses coming into the circuit will not be fast enough to prevent the lµF capacitor from discharging via the parallel 220kQ resistor. Thus, pin 2 of ICZa will be high and this high is then inverted by ICZb after a brief delay to produce a low on one input of a wired OR gate consisting of D7 & D8. If either input of the wired OR gate is low, pin 9 of IC1e is also low and transistors Q1-Q4 are all off. And when the transistors are off, the parking light and headlight relays (RLYl & RLYZ) are also off. i! ~ ~~~s ... C> <Oc, a:Es ~WMW c ... ;! ~S: v--+---~ti~5 -i---e~~~ QX a: ) c.:> ,. -✓ -, ca;3 N-- + ... I ~g C> C> c;:1; ::!: ffi~ a:,-.. Q ,- "' ::, :: o=:::;. z 0 + + I ....... . > + I ~ ~; c., ~E <O :!: u ., :5"' C>. .... N ~ "' !,! + c., "' H•· ~ I . ► a: 5. H•· M =(] 0 ~ C> C> ~ 0 == ~ 0 il: ::l+ ,- ~~.~~ Light sensing circuitry 8 '-' Now let's consider the light level sensi11g circuitry. During daylight hours, the resistance of the LDR is low and this holds pin 9 of IC1e low via inverters IC1c, IC1d and diode DB. Thus, pin 8 ofICle will be high, which means that the transistors and relays will all be off as before. When the light level falls, the resistance of the LDR increases and a logic high is now applied to pin 3 of IC1c. Pin 10 of ICld now switches high (after a delay set by the RC time constant on pin 11) and thus pulls the cathode of D8 high. If the engine is off, the other input of the wired OR gate (ie, the cathode ofD7) will be held low and no further circuit action takes place. However, if the engine is running, D7's cathode will also be pulled high and so pin 9 of IC1e will be pulled high by its --- ::l · + ,,,. I-to :::l M .., ., N !,! _H•· 0 a: w Q!... .... ..J ..J 0 a: I- z ~ 0 0 ... .,._ ea> en z I- ::c ..c;... c., :J C <( w ::c 0 + ~ I ....... Fig.1 (right): the circuitry from D1 to IC2a determines whether the engine is running, while the LDR, IClc & ICld monitors the light level. If the engine is running & the light level is low, the cathodes ofD7 & D8 are both held high & ICle turns on Ql & Q2 to activate the parking lamps relay (RLYl). This also turns on Q3 which then switches on Q4 & RL Y2 after a 1.5-second delay via IC2c & IC2d. :E 0 I::> <( . + > + I ~ w ~~g~ ~ff:c.:>ffi z ,- --' a: ::z:wOa: ; 35ffig ., JA N UARY 1992 29 ~~ ~1®·~7re~· lG ~='"Tte®~~~®~•! ·TC :;! TO _.,__. LOR ........!.... :;! ~o F ffl1 -l:::!i I~ I To~O S1 - - - ~ Q _001 - Q+t1 47uF + (e(_}• 1uF ~ - --<e:::>-eoa 1M~- • -0:::U D7.-cl)1 ~ 1 Ie eQD ~2 - N • +12V FROM BAITTRY VIA 15A FUSE C• ~Lti1 BJ• 0001 + A----, {:illJt ~ <Clt '-f ~ ~ 01 ~~---~ ~ '-,J.0,33 • tOli]e RELAY RLY1 · k D11.a::::::,..~ D 10k ~ •01 ill 4584 N • t I •041 uF ~ t;) f'!\REG1 I ~ +~j01 100.F-1 TD PARKING LIGHTS TO C ASSIS Fig.2: install the five wire links on the board first & note particularly the link underneath IC1. The remaining parts can be installed in any order but take care with the orientation of polarised components. Transistor Q4 must be mounted with its metal face towards IC2 (see Fig.1 for pinout details). associated 100kO resistor. Thus, pin 8 of ICle switches low and turns on Ql, Q2 and relay RLYl to activate the parking lights. Now let's see how the headlights are turned on. When Q2 turns on, Q3 also turns on and takes pin 5 of IC2c high. This in turn switches pin 8 of IC2d high after a 1.5-second delay, as set by the RC time constant on pin 9. Thus, Q4 turns on and activates RLYZ which then supplies power to the headlights. Q4 also turns on LED 1 to indicate that the lights are on. The reason for the 1. 5-second delay is to limit the surge current that occurs when the lights are turned on. This would obviously be very much higher if both sets of lights were turned on at the same time. The RC time constant at the output of IClc provides about 20 seconds of delay when night/day transitions are detected. This eliminates false trig- gering due to short variations in the light level falling on the LDR. Further filtering is provided by the l0µF capacitor on pin 3 of IClc. Switch S1 and IClfprovide the 30second "temporary-on" feature. When pushbutton switch S1 is pressed, the associated lO0µF capacitor quickly charges via a 1.5kO resistor. The resulting high is then inverted by IClc and pulls pin 3 of ICZb low via Dl 1. This logic low makes the circuit think that the engine is running and so, if it is night time, the lights turn on. The lO0µF capacitor then begins discharging through its parallel 330kO resistor and, after about 30 seconds, pin 6 of IClf switches high again and the lights turn off. Power is derived from the 12V car battery via reverse polarity protection diode D6 and 3-terminal regulator REGl. This gives a regulated +8V rail to power the circuit but note that the relays are powered directly from the +12Vrail. ZDl and its associated 1000 resistor provides protection against spikes which may be present on the supply rail from the battery. Relay ratings Tests on several makes of car showed that the parking lights draw from 4-9A, depending on the number of lamps in the circuit. For this reason, RLYl is specified with 10A contacts. The headlights, however, are a different proposition. Most high-beam lights are rated at 60-lO0W. Ifwe consider that there are two of them and the supply voltage is around 14V, it follows that together they draw around 14A. That is why a separate headlight relay with 30A contacts is used to switch the headlights. Construction Fig.2 shows the wiring details for the Automatic Headlight Controller. Check the PC board carefully to ensure that no track faults exist before you start construction. In particular, check for shorts between close tracks and for breaks in tracks. Once this has been done, start the assembly by installing the five wire links. One link runs under ICl, so ensure that it is installed before the IC is soldered into place. This done, install the resistors and capacitors but take care with the electrolytic capacitors as they are polarised. Next, install the diodes, transistors and ICs. Once again, take care with the polarity of these components and be sure to use the correct device at each location. Note that the metal face RESISTOR COLOUR CODE 0 0 0 0 0 0 0 0 0 0 0 0 30 No. Value 4-Band Code (5%) 5-Band Code (1%) 1 1 2 1 4 470kO 330kO 220kO 150kO 100kO 47kO 15kO 10kO 2.2kO 1kO 1000 yellow violet yellow gold orange orange yellow gold red red yellow gold brown green yellow gold brown black yellow gold yellow violet orange gold brown green orange gold brown black orange gold red red red gold brown black red gold brown black brown gold yellow violet black orange brown orange orange black orange brown red red black orange brown brown green black orange brown brown black black orange brown yellow violet black red brown brown green black red brown brown black black red brown red red black brown brown brown black black brown brown brown black black black brown 3 1 3 1 4 1 SILICON CHIP PARTS LIST 1 PC board, code CE 91 AL 1 12V PC-mounting relay (MR301 12HS) 1 12V 30A automotive relay 1 momentary contact pushbutton switch 1 plastic jiffy case, 130 x 68 x 41mm 1 plastic jiffy case, 83 x 54 x 28mm (to house S1 & LED; optional, see text) 1 light dependant resistor (LOR) The PC board can be held in position in the case using foam rubber. Use plastic cable ties to bind the leads into neat bundles & make sure that you wire the unit into your car in a professional manner, as described in the text. of the BD437 transistor (Q4) fac es diode D10. The 3-terminal regulator and the relay are the last components to go on the board. Once these are on, go over the board carefully and check that all parts are in their correct locations and are correctly oriented. The external leads can now be soldered to the board. Make sure that all leads have sufficient length to reach the relevant parts of the vehicle when the project is installed. For the prototype, we installed the pushbutton switch (S1), the LED and the LDR in a separate small zippy box which was then mounted on top of the dashboard. Bench testing Before installing the project in the car, it should be tested on the bench using the following procedure: . (1). Connect the unit to a 12Vbench power supply (more than likely nothing will happen) and make sure that the LDR is in bright light. (2). Wait 45 seconds for the circuit to stabilise, then press S1. Again nothing should happen. Now cover the sensor with a dark cloth, wait for another 45 seconds and again press S 1. This time RLYl should come on, followed about 1.5 seconds later by headlight rely (RLYZ) and LED 1. Check that the relays automatically switch off after about 30 seconds (first RLYl and then RLYZ 1.5 seconds later). (3). If all is well so far, connect an audio oscillator to the input and feed in a 50Hz 5V (approx.) pulse waveform. If the LDR is in bright light, the relays should remain off. Cover up the LDR and check that the relays and LED 1 switch on after the 45-second delay. If this is OK, disconnect the pulse generator and check that th e relays switch off after a short delay. If everything checks out as d escribed above, the project can be installed in the car. If you strike trouble , then refer to the troubleshooting procedure at the end of this article. Installation The position of the LDR is very important and will determine the effectiveness of this project. In the prototyp e installation, the LDR was mounted on the back of a small plastic case that also contained the pushbutton switch (S1) and the LED. This box was then mounted on top of the dashboard so that the pushbutton switch could be easily reached by the driver. One thing to watch is that the LDR must be shielded from oncoming headlights an d overhead street lights, otherwise the unit could switch the lights off at the w rong time. Similarly, it should also be shielded from any instrument lights, from the lights of following vehicles and even from the headlight indicator LED on the front panel. The final position of the LDR will, of course, vary from car to car. In stubborn cases, try mounting it under the dashboard to the right of the steering column. Semiconductors 2 4584 hex Schmitt trigger inverters (IC1 ,IC2) 1 78L08 3-terminal regulator (REG1) 2 BC558 PNP transistors (Q1-Q3) 2 BC548 NPN transistors (Q2-Q4) 4 1N4004 power diodes (D1,D6,D9,D10) 7 1N914 signal diodes (D2D5,D7,D8,D11) 1 15V 1W zener diode (201) 1 green LE:D (LED1) Capacitors 2 100µF 16VW electrolytic 2 47µF 16VW electrolytic 3 10µF 16VW electrolytic 1 1µF 16VW electrolytic 4 0.1 µF 5mm-pitch monolithic 2 .0033µF ceramic Resistors (0.25W, 5%) 1 470kQ 1 15kQ 1 330kn 3 10kQ 2 220kQ 1 2.2kQ 1 150kQ 41kQ 4100kQ 1 100Q 1W 347kQ Miscellaneous Automotive connectors, hook-up wire, 30A hook-up wire (for headlight wiring), nuts and bolts. The PC board can be housed in a plastic jiffy case and installed behind the dashboard, with the necessary wiring run through the firewall via a suitable grommet. To connect the parking lights into circuit, simply connect the lead from the PC board to the positive lead running to one of the lamps (the parking lamps are all in JANUARY 1992 31 Headlights Reminder Circuit If you don't like the idea of automatically switching your lights on and off, or you just want to save money, why not use the circuit as a Headlights Reminder instead? The modifications are straightforward and, as a bonus, the installation is much easier. A practical Headlights Reminder should sound a warning buzzer when three conditions are satisfied: (1) the engine is running; (2) the light level is low; and (3) the headlights are off. We already have the engine and light level sensing circuitry, so all we need to do is detect whether the headlights are on or off. This can be done using IC1f. The modifications to the circuit are as follows: . , . , . parallel, so energising one energises the lot). The external 30A headlights relay (RLY2) can be mounted in the engine bay, preferably adjacent to the existing headlights relay. It's then simply a matter of identifying the leads and connecting the normally open contacts ofRLYl across the normally open (1 ). Disconnect the anode of D11 from pin 3 of IC2b and connect it instead to pin 9 of IC1 e. (2). Reduce the 100µF capacitor on . pin 5 of IC1f to 0.1 µF and increase the 1.5kQ resistor to 100kQ. Delete switch S1. (3) . Substitute a 12V buzzer for RLY1 (ie, connect it between the + 12V rail and the collector of Q2). Leave diode D9 in position. (4) . Delete all components following Q2 and the buzzer, except for the 47kQ resistor on pin 5 of IC2c and the 150kQ resistor on pin 6 (these resistors are left in circuit to prevent the Schmitt triggers from oscillating). If you are uncertain as to which parts to leave out (or are too lazy to work it out), just leave out Q3, Q4, LED1, D10 and the external relay (RLY2). contacts of the existing relay. You can do this quite easily by using double adapter automotive spade clips. Note that any wiring between the two relays must be run using 30A automotive cable. Don't forget to connect the leads from the PC board to the coil terminals of RLYl. The connection to the ignition coil That's all there is to it. To install the unit, connect it to the ignition coil as before and connect the free end of the 100kQ resistor at IC1f to the switched side of the headlights switch. The + 12V supply for the circuit should be picked up from the switched side of the ignition switch, via one of the existing fuses (this is possible because the circuit now draws negligible current and doesn't have to be permanently powered). Now, when it's dark, your engine is running and the lights are off, the cathodes of D7, D8 & D11 are all high and IC 1e turns on Q1 & Q2 to drive the buzzer. When you turn your headlights on, IC1 f's output goes low and pulls pin 9 of IC1 e low via D11. IC1 e's output thus switches high, Q1 & Q2 switch off and the buzzer stops. can be made by terminating the input lead with an automotive eyelet lug. Power for the circuit must be obtained directly from the battery side of the fusebox via a 15A in-line fuse. Don't use any of the existing fuses and make sure that the supply remains at+ 12V even when the ignition is switched off (note: once installed, the circuit is powered continuously). Also, don't leave out the 15A in-line fuse; if you do, you run the risk of a fire if there is a short circuit. If you are joining wires to existing cables, it's best to solder the junction and then insulate the soldered joint with a few layers of insulation tape. Make sure that no strain is placed on any cables running through the car and that no metal can wear through the cable insulation. Troubleshooting We mounted the LDR on the rear panel of the control case but this can be varied to suit your situation. Note that the LDR must be mounted where it will not be exposed to oncoming car headlights, or to street lights or instrument lights. 32 SILICON CHIP Hit doesn 't work, the first step is to check component placement, orientation and soldering. If these checks don't reveal anything, the next step is to isolate the faulty circuit section. The procedure is as follows: (1). Check the supply voltages, You should get a reading of +8V at the output of REGl and on pin 14 of each IC. Check also that +12V is being supplied to each relay coil. Switch off immediately and clear the fault if you don't get the correct readings. (2). If the supply voltages are correct, remove diodes D7 & DB and check that both relays turn on. If neither relay turns on, check the circuitry around ICle, Ql and Q2. IfRLYl turns on but not RLY2, check the circuitry around Q3, IC2c, IC2d & Q4. (3). If both relays turn on in step 2, you've cleared the circuitry following ICle. Now install DB and check that the relays are off when the LDR is exposed to bright light (note: you may have to wait while the 47µF capacitor on pin 11 of ICld discharges) . If the circuit passes this test, cover up the LDR and check that the relays switch on after 45 seconds. Check the circuitry around the LDR, IClc, ICld & DB if you strike problems. (4). If everything is OK so far, then the fault lies in the engine sensing circuitry. Install D7 and try pulling pin 1 ofIC2a high (ie, connect it to the +BV rail). Provided the LDR is covered up, the relays should close after a short delay. If they don't, check the circuitry around IC2a & IC2b. If they do, try pulling pin 13 of IClb low. If the circuit still works, check ICla and Where to buy the kit A kit of parts for this project is available for $32.95 plus $3.50 p&p from CTOAN Electronics, PO Box 33, Condell Park, Sydney, NSW 2200. Phone (02) 708 3763. Orders may be placed using Bankcard, Mastercard, cheque or money order. The kit includes the PC board, all on-board components, the pushbutton switch, the LED, the LOR and the on-board parking lamp relay. It does not include the plastic cases, headlight relay, cable or automotive connectors. These parts may be purchased from electronics retailers and automotive accessory shops. If you are unable to get the project going, CTOAN Electronics offers a full baekup repair service. The cost is $15.00 plus $5.00 return postage. Please note that only kits built as described in this article and with good qualit soldering can be accepted for repair. Note: copyright of the PC board associated with this project is retained by CTOAN Electronics. its associated components, otherwise check the circuitry around IClb. Finally, there are a few simple adjustments you can make to the circuit if necessary. If the circuit turns the headlights on too early, increase the value of the lOOkQ resistor in series with the LDR. Alternatively, decrease the value of this resistor if you want the lights to come on earlier. The "TEMPORARY ON" period can be adjusted by changing the 330kQ resistor on pin 5 of IClf. Increase the value of this resistor to obtain a longer period and decrease it to obtain a shorter period. For example, reducing the resistor value to 150kQ will give a period of about 15 seconds. SC Introducing the Protel advantage. Protetf or Windows': Protelfor Windows is an entirely new Printed Circuit Board design system createdf or Windows 3. Prate!for Windows brings the prof essionalism ofProtel's proven PCB design sof tware to the highly productive Windows 3 environment. New Protel users will start designing sooner and experienced users will work more efficiently than ever. In 386 advanced mode, Windows 3 provides virtual memory capability, which allows advanced PCB users to design without restrictions on the total number of components, nets, tracks, etc. Protel f or Windows supports the multiple document • Copper Trace Layers-81Top □ Midl Ill D Mid 8 - □ Mid9 --, 0 Drill Guide D Drill Draw L81 Keep Outs □ Mid 3 0 Mid 4 □ Mid 11 Ill □ Mid 12 □ 0 □ Mid 13 - Mid 5 0 Mid 6 D Mid 7 D - □ Mid 14 111111 81 Bottom 0 Ill Ill □ DRC Errors 81 Grid 1L'.J Ill D Rats Nest Ill L8l Grid 2- B Selections D Ill M [8] Transparent hanical Layers ech 1 ech 2 I [Silks Ill D Bottom Ill . L8l Tc rsMT Paste Mask Visible 81 Multi Layer EJ Background ISolder Mask I □ Top III D Bottom LD Top inteiface (MDI) standard. Any number offiles can be loaded ••• - -- -- ----, - 0 lU 0 Ill llJl!]0Mid10 i Special - ~ lllll D Mech 3 II D Dithered Colors B D Mech 4 - ... at the same time, using standard Windows routines, to move information between different files or different applications. Tbe Protel for Windows family consists of Advanced PCB advanced level PCB layout -$1990. Options. Advanced Place $995, Advanced Route $995. Professional Scbematic' - schematic capture -$1295. Option: Digital Simulator* $795. Selecl P1inte1 IPostSc,i?I Printe r on LPTl: Balch Mode 0 0 Separate Page Fm Each Print Composite Prinl <at> Panels [Multiple La}'ers Per File) ~ X Conection ~ YConeclion ■ Te cb u o togy Scale PrintScale Protel Technology Pty Ltd PO Box 204, Hobart Tasmania 7001 Phone (002) 730100 Fax (002) 730944 Toll-free 008 030 949 ~ ~~ Avallable April 1992. Protel is a lr!f<istered trademark. Adva11ced PCB and Professional Schematic are registered trademarks of Prate/ Technology Ply Ltd. \Vinduu,'S is a registered trademark of Microsoft Co,poration Inc. 1 JANUA RY 1992 33