This alarm activates when the illumination level changes from almost total darkness to a moderately high illumination level. When this happens the alarm is locked and the alarm signal, be it a light or a sound, remains active.

How to make a Light Sensitive Sound Generator Circuit?

An oscillator circuit may have many applications. The diagram below shows how to make it work as a light sensitive sound generator using a LDR and a 741 operactional amplifier.

Light activated switch circuit with LDR and Operational Amplifier.

This circuit has many applications. It could act as a photocell and switch off a light in a room or turn on the radio when it is dawning, etc.

Refrigerator door alarm circuit with two 555 timers

This refrigerator door alarm circuit alerts you when the door has been left open. Very important, because the power consumption increases when this happends. It uses the popular 555 timer IC

Dark detector circuit using LDR and relay

This circuit uses, as a main component, an LDR (photoresistor). An LDR changes its resistance value depending on the amount of light it received. The more light means less resistance, the less light means more resistance.

Light Operated Relay Circuit using LDR.

The LDR varies its value (ohms) depending on the amount of light that illuminates it. The more light less resistance and less light more resistance, A potentiometer is used to control the light level that activate the relay

Shadow detector alarm circuit with two LDRs

This circuit detects if there is a difference of lighting between two LDRs, and sends an audible and visual warning. Circuits that use two LDRs are more reliable than those that use only one.

Automatic night light using 555 and relay

This Automatic night light using 555 IC turns lights on when there is no daylight. The circuit is perfect for lighting single places such as the garden, the front door of the house, the entrance to the garage, etc.