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

It is very important to correct the faults in the electrical system of an automobile or motorcycle or other, as soon as possible. This circuit will warn us when this happens.

This 2 LED Temperature change indicator 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.

Rain detector using two transistors

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

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.

This darkness detector circuit beeps when the light drops below a certain level.

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.

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

This light detector circuit activates a lighting device through a relay when the intensity of the daylight is no longer sufficient.

It can be used to illuminate the main entrance of the house, a showcase that must be kept lit at night, an unsafe area at night, etc.

Photodiode Amplifier – Current to Voltage Converter.

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

Electronic sound control circuit (applause)

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.

Twilight switch circuit with Op. Amp.and LDR

This Twilight switch circuit activates a light, a lamp, a motor, etc., at the time of sunset and performs the reverse process at dawn.

This is an ideal circuit for activating a security light that must be on all night.