Homemade tap alarm

TP-IP4220CZ6 5V 0.35PF breakdown voltage 6V SOT

RF cable can be customized for other specifications

The core device of the alarm described in this paper is a commonly used 555 time base integrated circuit, plus several peripheral components, which constitute a high sensitivity trigger delay circuit.

Circuit principle: The trigger signal is input by 2 feet. After triggering, flipping and delaying, the control voltage is output by 3 feet. The maximum load current is 200 mA, which can directly drive small and medium power loads. The sensitivity of the circuit can be adjusted by adjusting the resistor R1. The value of R1 is small, the sensitivity is low, and the value is high. The length of the delay time is determined by R3 and C2. The larger the value of R3 and C2 is, the longer the delay time is. The circuit's supply voltage range is 5 to 18V, and the static power consumption is less than 10 mA. When someone knocks or breaks the glass, the sensor B attached to the glass is immediately detected and sent to the NE555's 2-pin pulse signal. The 3-pin output voltage directly drives the relay K to pull in, and the normally open contact control alarm jobs.

The requirements of the circuit for components are not strict. As long as the leakage of capacitor C1 is small, C2 can be selected from tantalum electrolytic capacitors. The circuit is installed without any debugging and can be operated with power.