Dark detector circuit
Description.
The dark detector circuit shown here can be used to produce an audible alarm when the light inside a room goes OFF. The circuit is build around timer IC NE555.A general purpose LDR is used for sensing the light. When proper light is falling on the LDR its resistance is very low. When there is no light the LDR resistance increases. At this time the IC is triggered and drives the buzzer to produce an alarm sound. If a transistor and relay is connected at the output (pin3) of IC1 instead of the buzzer, electrical appliances can be switched according to the light.
Circuit diagram with Parts list.
Notes.
- The LDR ,R4 can be any general purpose LDR.
- The circuit must be assembled on a good quality PCB or common board.
- The circuit can be powered from a 9V PP3 battery.
- The POT,R3 can be sued as a volume controller.
- Mount the IC1 on a holder.It will make replacements easy.
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What are the possible transistor and relay that can be replaced instead of the buzzer?
hi sir
iremove the buzzer and i put transistor , RLL and light
note : the light is on and off when i coverd the ldr ( no light high ressistor
Hi Abdullah NE555 can drive up to 300mA load. So you can use a power relay in the place of Buzzer remove variable resistance volume control donot forget the freewheeling diode across the relay coil. and connect any load through its contact. When you cover LDR the resistance will go high and voltage at Pin 4 will go high the out put of NE555 will go high hence the relay will come on, you may use an LED with 1K resistance in series in parellel to the relay as an indication..