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555 time limiting lock alarm device circuit

2017-01-07 07:54  
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555 time limiting lock alarm device circuit
As the figure 15-21 shows, the door lock alarm device is composed of the monostable trigger circuit, the timer and the alarm sound circuit.etc. It has the function of time limit, so it can be used as the subsidiary part of the door lock. The touch trigger is composed of the IC1(555) and R1, C1, C2.etc, the sequin M which is connected with pin-2 connects with the metal part of the door lock, when someone uses opens the lock, the human body sensor signal will set the IC1, Vt1 conducts and VT2 cuts off. C4 is charged through R4. The monostable timing circuit is composed of the C4, R4 and IC2(555), when C4 is charged to the 1/3VDD=1.5V, IC2 sets and VT3, VT4 conduct to open the IC3's power supply. IC3 uses the four stereo analog manifold KD9561.