Door Knock Alarm With Timer

Description

This Knocking Alarm With Timer uses the piezoelectric element of a piezo buzzer as the input sensor. The piezoelectric element plate is a patch at the center of the door wing by using cello tape. Apply a small quantity of adhesive at the edges between the plate and the door. The Alarm With Timer is designed with extending wires about 1-1.5 meters from the piezoelectric to the circuit. IC NE555 is configured in monostable mode.

When this Low-cost Timer Circuit gets an input pulse, its output goes high for a period set by the Variable resistor, resistor, and capacitor. IC UM66 is used as a melody generator. When the door is knocking at the pizza plate generates an input pulse, which is amplified by the transistor. The Door Knock Alarm's amplified signal triggers the timer IC NE555 and its output pin 3 goes high to enable the melody generator. After the set time period, the melody sound stops.