This circuit activates a lighting device through a relay when the intensity of daylight is no longer sufficient. Good for illuminating the main entrance of the house, a display case that needs to be kept lit at night, an unsafe area at night, etc.

This single transistor blown fuse indicator circuit warns us by lighting a LED when there is a problem in an electrical installation protected by the fuse.

Light Sensitive Sound Generator Circuit – An oscillator circuit may have many applications. The diagram shows how to make it work as a light sensitive sound generator using a LDR and a 741 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.

This circuit shows us, by means of two LEDs, when the sensed temperature is above or below a set limit. When the temperature is above the pre-set temperature level, LED D1 will light up and if it is below, LED D2 will light up.

Circuit that aims to alert the beginning of the rainfall. Its few components make it an interesting and easy project.

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.

The main elements of this circuit are the 555 integrated circuit, working as an astable multivibrator and an LDR which is used as darkness sensor.

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

Very simple circuit that amplifies the current signal generated by a photodiode and transforms it into voltage with a controlled gain

This electronic sound control circuit works like a sound activated relay and can activate or deactivate a device connected to it, by two consecutive claps.

This Twilight switch circuit activates a light, a lamp, a motor, etc., at the time of sunset and performs the reverse process at dawn.
The is an ideal circuit for activating a security light that must be on all night.