Electronic GateKeeper circuit

Published:2012/9/25 21:41:00 Author:muriel | Keyword: Electronic GateKeeper | From:SeekIC

This circuit can do the job of a Gatekeeper and intimates you if someone passes through the gate. The alarm can be an AC bell or a Lamp. The alarm turns on for 1 minute and stops if the light barrier is restored again.Infrared rays are used as the light barrier to activate the alarm system based on a Phototransistor. The high gain NPN Darlington phototransistor L14F1 conducts when its face is illuminated with IR rays. This brings its collector to ground potential. IC1 is used as a simple voltage comparator with a potential divider R2 and R3 connected to its inverting input. So that half supply voltage (6 volts) is available to its inverting input. Its non inverting input is connected to the collector of the phototransistor. Normally the output of IC1 will be low since T1 is conducting. When the IR beam breaks, the collector of T1 becomes high and the voltage at the non inverting input of IC1 increases above the voltage at the inverting input and output becomes high. This triggers the relay driver T2 and relay turns on. Capacitor C1 gives a short delay at the non inverting input of IC1 to prevent false triggering. Capacitor C2 keeps the base of T2 high for a short time even if the IR rays restore. Electronic Gate Keeper Schematics



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