Lock control anti-theft alarm circuit diagram

As shown in the figure is the lock control anti-theft alarm circuit. The circuit consists of RS flip-flop, gated oscillator, alarm circuit, etc. The RS flip-flop is composed of NAND gates F2 and F3, and the gated oscillator is composed of integrated circuit TWH8751 and R and C.

When SKK is in the "lock door" position, input terminal 2 of NAND gate F1 is high level, and F1 directly reflects the status of DBK1-n. If one of DBK1-n is open, F1 outputs low level. Set the RS flip-flop to "1" (Q is high level, Q is not low level), the corresponding strobe pin ② of TWH8751 is low level, triggering the oscillator to start oscillating, and the oscillation signal causes the speaker to sound an alarm.

When SKK is in the "open" position (that is, using the key to open the door lock normally), the input terminal pin ② of F1 is low level, so the input terminal of F1 is blocked and the RS flip-flop is reset (Q is low level, Q is not high level), correspondingly TWH8751 will not oscillate because the strobe pin ② is high level, and the alarm will not work. At this time, the owner can use all the items monitored by DBK1-n at will. When the owner locks the door and leaves, the alarm will automatically resume normal operation. When extinguishing the alarm, first use the key to unlock the door and then press AN.