The touching vibration alarm consists of touch trigger circuit, vibration trigger circuit and alarm circuit. The 555 time base circuit U1 forms the typical monostable operating mode. The transient time is determined by the values of RP1, R2 and C2.
Usually the circuit is in steady state, 555 time base circuit 3 pin output low, the alarm chip does not alarm because there is no power supply. When the human touch the electrode sheet M, the human body induced by the clutter of the signal injected into the 555 trigger pin 2 through C1, or vibration sensor S1 connect instantly because of the vibration, will both cause the U1’s pin 2 to appear instantly low level , So that the 555 circuit flip into the transient, pin 3 mutate to high level, alarm chip works.
Transient time is over, the time base circuit back to steady state, stop the alarm. The length of the alarm time can be adjusted by changing RP1. LED is a two-color light-emitting diodes, green LED bright after power, use as the power indicator light, the red and green light are bright and shows the overall orange when alarming, the resistance of resistor R5 determines the alarm sound play speed, generally take 180K-240K, pay attention to install the resistor before installing the chip, the entire circuit can work under DC 3-6V.