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Doorknob Proximity Alarm for wooden door

2015-03-01 13:18  
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Doorknob Proximity Alarm for wooden door
Reverse engineered circuit diagram of a popular retail doorknob alarm. It contains a small transmitter and the doorknob acts as an antenna so it will not work on a metal door. When a person comes close to the doorknob this loads down the oscillator and the alarm sounds. The proximity sensor circuitry is perfectly capable of driving 74HCT series CMOS logic in place of of the sound effect IC's shown in the circuit diagram.