INDEX

Bulgar Alarm

Here is another circuit which can be called as a basic burglar alarm. So when a thief passes a way it cuts the light and resistance of LDR increases to make the buzzer to beep. Here i put 10Kohm resistor because the value of resistance of the LDR is around 10Kohm. First test the value of LDR
resistance and put the resistance so that when light is there the transistor is cut off and when dark the voltage drop increases and transistor become saturated and the buzzer beeps Normal buzzer beeps when voltage >7V mostly. See the relay troubleshooting. Mostly relays are of 6V and 12V. Be
careful about that. The resistance in series with LED should be proper so that LED will not be burned.

This is a circuit which is used to switch on an equipment when the intensity of light is less. An LDR is a device whose resistance decreases as light increases. So adjust 10Kohm resistance so that, equipment will turn off when the light intensity is above desired level(this level is set by you). This circuit can be used for automatic switching of streetlights.