How to make very Simple Electronic Dark or Light detector circuit using LDR and Integrating a Relay in it for making it a Automatic Switch.
By: Alok kumar
Today we are going to learn how to make an eletronic dark or light detector circuit because this marvelous piece of gadget can be very useful if integrated with other devices as a switch. It means when a certain predefined intensity of light is reached our device is able to detect that condition and able to switch any device and can be very useful for saving energy and efforts. We can make a Automatic Lawn Light, Automatic Bulb or Tubelight, Automatic Car Head Light switch and many many useful circuit. It can be used in various ways if logically applied.
So lets get started without wasting our time...
What is LDR (Ligt Dependent Resistance):
Light Dependent Resistors (LDR) is also called photoresistors because these are made of high resistance semiconductmaterialor . When light hits the device, the photons gives electrons energy
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to become mobile. This makes them jump into the conductive band and thereby they conduct electricity as a conductor.
For more info search this item on wikipedia there you will find every thing about LDR.
Component Required:
Battery: 6volt battery any.
Resistors: 330ohm one.
Pot: 100kohm pot or preset.
Transistor: BC-547.
LED: one led for indicator.
Relay: 6v relay. for switching operation.
Circuit diagram:
1. For Dark Detector ciruit using LDR.
Simple electronic Dark Detector or Sensor circuit using LDR
Working of above light or Dark detector circuit:
When there is light present, the LDR has low resistance. So the voltage at the base of the transistor is not high enough to turn the transistor on.
Therefore, no current will go from the collector to the emitter of the transistor. All the current will instead pass through the potentiometer and the LDR.
When there is dark, the LDR has high resistance. This means that there will be a voltage drop over the LDR. If we look at the circuit diagram then we will see that the LDR is connected from the base to the emitter of the transistor.
This means that we will also have a voltage drop from the base to the emitter. And we know that this is what is needed to turn the transistor on.
So since the transistor is turned on, current will pass through 330ohm resistor, the LED and from collector to the emitter of the transistor. This will make the LED turn on.
How to transform Dark detector circuit into light detector circuit:
Just interchange the LDR and 100k pot. Then it will become the simply Light Detector circuit.
How to make above circuit a LIGHT DEPENDENT SWITCH using Relay:
Just remove R1 and D1 and insert 6v Relay instead ogf them, then this above simple circut become a LIGHT DEPENDENT AUTOMATIC SWITCH
Final product:
Dark or light detector circuit using LDR.
Thank you for reading.
