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The door lock alarm with the time recognition function

2017-01-07 11:38  
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The door lock alarm with the time recognition function
The circuit is shown in figure 1, which is composed of the 555 time-based integrated circuit and alarm integrated circuit. The time-based circuit IC1 consists of the temporary single steady trigger of T=4min or so with R1 and C1. Usually, IC1 is in the stable state, and the 3-pin of it outputs a low LEV, VT1 is blocked, VT2 is conducting, the capacitor C2 is shortened by VT2 and can't be charged, the 6-pin on the threshold of the time-based circuit IC2 is in a high LEV, while 3-pin is outputting a low LEV, the alarm sound integrated circuit IC3 is not working without power, the loudspeaker is silent. M is the touching electrode chip which is linked to the lock.