Tiny Locker Guard. Beginner’s Trial 4

Make this Tiny Locker guard and Thwart the attempt of Burglary. This tiny circuit beeps when the door of Locker or Almirah opens in daytime. It beeps a few minutes after the light enters into the locker as a trick to confuse the burglar. It uses LDR as the light sensor.

Working of the circuit is simple. When the LDR is in dark, it never conducts so the circuit remains standby. When the LDR gets light, it conducts and C1 starts to charge. When the voltage in C1 increases above 4.7 volts, Zener diode ZD conducts and switch on T1. Buzzer beeps till the door is closed again. Resistor R1 is provided to discharge C1 after LDR again enters into dark.

To make the circuit compact use a Mini buzzer (one used in UPS) and two 3V button cells.