InfraRed Proximity Sensor is widely used sensor module in robotics. They can be found in most simplest of robots like a Line Follower and the smart phones we use. Do you know what does the sensor do? If so, then how does it work? Let us learn the basics of the InfraRed (IR) Proximity Sensor.
An InfraRed Proximity Sensor is a circuit designed to sense and respond to change in proximity of an object in front of it, with the help of InfraRed Light.
The Transmitter, is basically an InfraRed Light Emitting Diode. It emits InfraRed Light whenever the sensor is powered. The emitted light falls on objects in front of it, just like when a flashlight is turned ON.
If there is any object in front of the InfraRed LED, then the light gets reflected and some of it comes back at the sensor and Receiver picks up the light that got reflected back. The receiver is an InfraRed Photodiode that detects the reflected IR light and changes its conductivity in Reverse-Bias. Higher the intensity of received IR light, higher its conductivity.
The Op-Amp is an integrated circuit designed for the purpose of amplifying and outputting the voltage difference between two input pins. One of its input is a reference or threshold voltage set by the potentiometer and the other input is the voltage through the photodiode.
When the voltage through the photodiode is lower than the set threshold voltage, then the op-amp is set to output LOW signal.
And, if the voltage through the photodiode is equal or higher than the set threshold voltage, then it outputs a HIGH signal.
Paul Pavish
INTERESTING FACTS:
An interesting fact about InfraRed Light is that, even though it is not visible to human eyes, it is visible to camera. That is why IR LEDs are used for lighting in Night Vision Cameras.
IR emitter in Mobile Phones 
IR emitter in sensor module
