Car Alarm

041 CAR ELECTRONICS The car alarm accepts signals from a variety of sources, includ- ing special sensors and the standard switches in a car, such as the door and ignition contacts. The unit has a relay output that en- ables controlling an acoustic transponder (loudspeaker, buzzer), light, a radio transmitter, and others. The alarm is remarkably simple to set, because all control func- tions are performed by a single switch. It is switched on after parking the car by closing S1 when the green LED lights to indicate that the driver has 13 seconds to leave the car. When this delay has lapsed, a yellow LED lights to indicate that the alarm is set. When any of the alarm sensors is actuated (which also happens when the rightful owner of the car opens a door), a red LED lights. ELEKTOR ELECTRONICS JULY 1989 SUPPLEMENT CAR ALARM D ...D4 = 1N4148 BC107 T1 930n BC107 BS170 1N4148 D3 1N4148 BS170 S + R TRG 1C2 THR NE555 DIS CV C8 10n 129 0 C9 C81 TO OP 189 Mr2r1 • OUT The relay will then...