IR SENSOR

What is IR Sensor?

An IR sensor is an electronic device, that produces in order to detect some parts of the environs. This sensor can measure the heat of an object and detects the motion. These sensors are used to measure only IR radiation, rather than producing it that is called as a passive infrared sensor. 

Generally in the IR spectrum, all the surrounding objects generate different form of thermal radiation.These kinds of radiations are not observable to our eyes, that can be sensed by an IR sensor. The emitter of the sensor is infrared LED and the sensor is an IR photo-diode which is sensitive to infrared light of the same wavelength as that produced by the infrared LED. When infrared light drops on the photo-diode, the resistances and output voltages change in proportion to the received magnitude of the infrared light.

Emitter, Infrared LED (Transmitter)

• IR LED is used to transmit infrared light on our circuit.
• An infrared light-emitting diode (IR LED emits infrared light not visible to the naked eye.

The wavelength and colour of the light produced depend on the material used in the diode. Infrared LEDs use material that produces light in the infrared part of the spectrum, that is, just below what the human eye can see. Different infrared LEDs may produce infrared light of differing wavelengths, just like different LEDs produce light of different colours.

Since the human eye cannot see the infrared radiations, it is not possible for a person to identify whether the IR LED is working or not, unlike a common LED. To overcome this problem, the camera on a cell phone can be used. The camera can show us the IR rays being emanated from the IR LED in a circuit.

Sensor, Photo-diode (Receiver)

• Photo-diode is used to capture a reflected of IR LED.
• When exposed to the light, a semiconductor diode will generates a potential difference or electrical resistance will changes

A Photo diode is a reverse biased silicon or germanium pn junction in which reverse current increases when the junction is exposed to light. When no light is incident on the pn junction of photo diode, the reverse current is extremely small. This is called DARK CURRENT.

When light is incident on the pn junction of the photo diode there is a transfer of energy from the incident light (photons) to the atoms in the junction .this will create more free electrons (and more holes) these additional free electrons will increase the reverse current.This electrical energy can be recorded as voltage drop fluctuations by using a series resistor in the outer circuit and taking voltage readings across it.

How is the line is sensed?

IR Line Sensors will follows lines or the light reflected on a surface. The sensor works by detecting reflected light coming from its own infrared LED. By measuring the amount of reflected infrared light, it can detect transitions from light to dark lines or even objects directly in front of it.

The sensor has IR light emitter and detector. The sensor returns the status of the IR light reflected from a surface as ON or OFF.  The LED shows the status of the sensor. It should be needed be calibrate the sensor to set the threshold between light and dark. The sensor also has a pontention-meter knob to adjust.

Depiction of the operation of an IR LIne Sensor to measure brightness

The IR emitter emits a constant IR beam. The white surface reflects most of the beam while the black surface absorbs most of the beam. This reflected beam is picked up by the IR detector and its conduction increases and hence a voltage variation in the output pin (0v for absence of IR rays and 5V for maximum intensity). This is given to the comparator to compare with a reference signal generated by the potentiometer. That is how the line is sensed by the sensors. 

Case 1(NORMAL) which is for sensor 2 is when the robot has to move forward as only the center sensor is low. Similarly Case 2(SENSOR 3) is towards right, Case 3(SENSOR 2) is towards left and case 4 is stop as all the sensors read high.