Learn Infrared Sensors Basics

1. IR SENSORS

2.  IR Sensor is an electronic device that measures and detects infrared
radiation in its surrounding environment.
 There are 2 types of IR sensor
 Active IR and Passive IR
Introduction

3.  Active IR
 These sensors both emit and detect infrared radiation.
 It has 2 parts
 LED(Light emitting diode) and A receiver
 When object comes closer to the sensor the IR light from LED reflects off
of the object and it is detected by receiver.
 These acts as proximity sensor and they are commonly used in obstacle
detection such as Robots
Introduction

4.  Passive IR.
 It only detect the IR radiation but do not emit it from LED.
 PIR are mostly used in motion based detection.
Introduction

5.  An Active IR sensor both emit and detect the infrared radiation.
 In IR sensor Transmitter simply an IR LED (Light Emitting Diode)And
Receiver is an IR photodiode that is sensitive to IR light of the IR LED
transmits the same wavelength as that is transmitted by the IR LED.
 When object comes near to the sensor the infrared light from the LED
reflects off of object and it is detected by the receiver
Principle

6. Circuit Diagram

7.  In this circuit transmitter which transmits continuous IR rays to be
received by an IR sensor module.
 Depending upon its receiving of IR rays IR output terminal of the receiver
varies.
 This variation cannot be analysed so this output is fed into the
comparator circuit.
 When the IR receiver does not receive a signal, potential at the inverting
input goes higher than that non inverting input of the comparator. Thus
the output of the comparator goes low. But Led does not glow.
Explanation :

8.  When the IR receiver module receives signal to the potential at inverting
input goes low, Thus the output of the comparator goes high and LED
starts glowing.
Explanation :

9. IR Interfacing with STM32

10.  IR LED Transmitter
In the range of infrared frequency IR led emits light . IR light is invisible as
its wavelength(700 nm -1mm) is much higher than the visible light range. IR
LED’s have light emitting angle of approx. 20- 60 degree. Few centimetres
to several feet's. Some transmitters have the range in Kilometres. Its
depends upon the type of IR transmitter and the manufacturer. IR LED
white or transparent in colour so it can give out maximum amount of light.
Features of the IR sensor

11.  Photodiode Receiver
Photodiode acts as the IR receiver when the light falls on it as its
conducts. Photodiode is a semiconductor which has a P-N junction
operated as in reverse bias. That means conducting the current in reverse
direction when Light falls on it and the amount of current flow is
proportional to the amount of Light.
This property is useful for IR detection. Photodiode looks like a LED
with black colour coating on its outer side. Black colour absorbs the highest
amount of light.
Features of the IR sensor

12.  LM358 opamp
LM358 is an Operational Amplifier is used as voltage comparator in the IR
sensor. The comparator will compare the threshold voltage set using the pre-set
and the photodiode’s series resistor voltage pin.
Photodiode’s series resistor voltage drop > Threshold voltage =Opamp output is
high
Photodiode’s series resistor voltage drop < Threshold voltage =Opamp output is
low
When Opamp’s output is high the LED at the Opamp output terminal turns on
(Indicating the Detection of the Object)
Features of the IR sensor

13.  Variable Resistor
The variable resistor used here is a pre-set. It is used to calibrate the
distance range at which object should be detected.
Features of the IR sensor

14.  Its response time is faster than thermocouple.
 It provides good stability over time.
 The battery used in infrared devices last for long duration due to lower
power consumption.
 No corrosion or oxidation can affect the accuracy of infrared sensor.
 It delivers high repeatability
Advantages of IR sensors

15.  Infrared waves at high power can damage eyes.
 It supports shorter range and hence it performance degrades with longer
distances.
 It supports lower data rate transmission compare to wired transmission.
 Infrared frequencies are affected by hard objects (e.g. walls, doors) ,
smoke, dust, fog, sunlight etc. Hence it does not work through walls or
doors.
Disadvantages of IR sensor

16.  Applications
 Infrared applied systems
 Transmission system
 Optoelectronic switch
 Infrared remote control equipment’s
 Smoke detector
 IOT (internet of things) application
 Industrial equipment’s
Application