LDR - Light dependent resistor circuit or light detector circuit using OpAmp LM358

Light sensor is a device which can sense the particular intensity of light and give indication like buzzer sound or LED glow. This function can be used as morning alarm or burglar alarm etc.

LDR - Light dependent resistor circuit or light detector circuit using OpAmp LM358

As we have already made an IR sensor circuit, In this project also we are going to use comparator circuit using LM358 IC.We are going to use one side as we need single side sensing task. In each port of this IC three pins are available which are non - inverting terminal PIN 2, inverting terminal PIN 3 and an output PIN 1. When voltage at non- inverting terminal is higher than inverting terminal the output gets high which means it will provide a voltage output as signal.

Pin diagram LM358

Circuit Diagram

Breadboard Diagram

Component required:

LM358 OP – Amp IC
Small LDR
10 KΩ Resistor
10 KΩ Potentiometer
White LED
220 Ω Resistor
Connecting wires
Power supply (9V Battery)

Working:

In above circuit we have connected pin 3 LDR (Light dependent resistor) which is non inverting terminal when light hits LDR sensor the ressistivity through it pins will be lowered and voltage supply will get high on the pin 3 which results as high output at PIN1 . In our requirement we want to make a variable sensing device so that we can manipulate the sensivity or set the value of intensity to be sensed . we add a variable resistor at pin 2. As the variable resistor is set for low resistance, the voltage on pin 2 gets high. The non- inverting terminal PIN 3 requires higher input signal to overcome the voltage on PIN 2 for higher output which means it is set for high intensity of light. As the resistance is improved the the sensivity of the sensor increases due to lesser voltage requirement in PIN3.

Application:

Simple Light Detector Circuit can be used in many applications like automatic switching of appliances up on detecting light, security systems, etc.
This circuit can be used in alarm system, where increasing intensity of light will trigger the alarm.
It can also be used in cupboards or wardrobesdoors which turns on the lights inside when door is opened.