Door Guard

Thieves often target lockedhouses. This door guard circuit detects any vibration in its vicinity when somebody tries to break open the door. The heart of the circuit is the piezo transducer (PZ1), which is the sensor element. If anyone attempts to open the door, the piezo element vibrates and the developed voltage drives transistors T1 and T2 into conduction. Now the alarm sounds for 20 seconds, which is taken care of by MOSFET T3 along with capacitor C1 and resistor R4 wired as a monostable timer. Learning: Application of UM3561 IC. Working of transistor as amplifier. Working of MOSFET BS170. Application of piezoelectric sensor. Brand: Kits'n'spares, Marketed by: Kits'n'spares