Light sensitive alarm using LDR

Light sensitive alarm using LDR

This light sensitive alarm is very simple and works using, as main components, a transistor, an LDR and a relay.

The 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.

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Light detector circuit using transistors and relay

Light detector circuit using transistors and 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.

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Twilight switch circuit with operational amplifier and LDR

Twilight switch circuit with operational amplifier 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.

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Dark detector circuit using LDR and relay

Dark detector circuit using LDR and relay

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.

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