HAVE YOU EVER FOUND YOUR CARbattery dead because you had left yourheadlights on after shutting off theengine and walking awa y? Before longyour battery is totally drained , and youhave to start looking for a passing goodsamaritan or a service station. It is afrustrating experience , as you know if ithas ever hap pened to you .

Th is circuit is designed to give off analarm anytime that the lights are on butthe engine off. The device is easy tobuild and almost any technique can beused. Installation is also simple and justtwo connections to your car's electri -cal system, and one to its chassis, arerequired for proper operation.

Th e circ uit for the project is shown inFig . I. An SPDT relay , RY I (RadioShack 275-003 or equivalent), and diodeD2 (IN4004 or equivalent) supply powerto the rest of the circuit only when theheadlights are on and the ignitionswitch is off. A circuit made up of R7and D I regulates the voltage to IC I.The IC is configured as an oscillator,and is used to supply pulses to QI,

NEW IDEASHeadlight Alarm

which is used as a transisto r switch.Each time a pulse from IC I reaches it,QI supplies power to TRl's driver cir-cuit (TR I is a piezo-buzzer element.Radio Shack 273-064 or equivalent ),sounding the alarm.

The connections to your car are fairlystraightforward. The lead marked TO+ 12V LIGHTS should go to a line thatcarries + 12 volt s whene ver the head-lights are on (the one for the dashboardlights is a good cho ice). The lead labeledTO + 12V IGNITION should go to one ofthe lines that power the car ' s acces-sories (radio . cigarette lighter, etc.).Make tho se connections to any pointthat is easily access ible ; typically thatwill be at your car's fuse box. The leadlabeled TO GROUND can be made to anyconvenient point that' s connected tothe car' s chassis.

Of course there are times when youwish to use your headlight s while theengine is off. All that need s to be doneto silence the alarm in tho se instances isto tum the ignition switch to the ACCES SORY position. -James Griggs

NEW IDEAS

This colu mn is devoted to new ideas,circuits, device applications, construc-tion tec hniques, helpfu l hints, etc .

All published. entries, upon publica-tion, will earn $25 . In addition, Panavisewill donate the ir model 324 Elect ronicWork Center, having a value of $49 .95.It combines the ir circui t -boa rd holder,tray base mount, and soider station (seephoto below) . Selections will be made atthe sole discretion of the editorial 'staffof Radio-Electronics.

R8 CP401 14.'K rct .TO

';"

+12V LLIGHTS + C3 110 K Q2BLACK

ZN222'ZA

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