What is an IR Sensor : Circuit Diagram & Its Working

IR technology is used in daily life and also in industries for different purposes. For example, TVs use an IR sensor to understand the signals which are transmitted from a remote control. The main benefits of IR sensors are low power usage, their simple design & their convenient features. IR signals are not noticeable by the human eye. The IR radiation in the electromagnetic spectrum can be found in the regions of the visible & microwave. Usually, the wavelengths of these waves range from 0.7 µm 5 to 1000µm. The IR spectrum can be divided into three regions like near-infrared, mid, and far-infrared. The near IR region’s wavelength ranges from 0.75 – 3µm, the mid-infrared region’s wavelength ranges from 3 to 6µm & the far IR region’s infrared radiation’s wavelength is higher than 6µm.

What is an IR Sensor/Infrared Sensor?

An infrared sensor is an electronic device, that emits in order to sense some aspects of the surroundings. An IR sensor can measure the heat of an object as well as detects the motion. These types of sensors measure only infrared radiation, rather than emitting it that is called a passive IR sensor. Usually, in the infrared spectrum, all the objects radiate some form of thermal radiation.

Infrared Sensor
Infrared Sensor

These types of radiations are invisible to our eyes, which can be detected by an infrared sensor. The emitter is simply an IR LED (Light Emitting Diode) and the detector is simply an IR photodiode that is sensitive to IR light of the same wavelength as that emitted by the IR LED. When IR light falls on the photodiode, the resistances and the output voltages will change in proportion to the magnitude of the IR light received.

Working Principle

The working principle of an infrared sensor is similar to the object detection sensor. This sensor includes an IR LED & an IR Photodiode, so by combining these two can be formed as a photo-coupler otherwise optocoupler. The physics laws used in this sensor are planks radiation, Stephan Boltzmann & weins displacement.

IR LED is one kind of transmitter that emits IR radiations. This LED looks similar to a standard LED and the radiation which is generated by this is not visible to the human eye. Infrared receivers mainly detect the radiation using an infrared transmitter. These infrared receivers are available in photodiodes form. IR Photodiodes are dissimilar as compared with usual photodiodes because they detect simply IR radiation. Different kinds of infrared receivers mainly exist depending on the voltage, wavelength, package, etc.

Once it is used as the combination of an IR transmitter & receiver, then the receiver’s wavelength must equal the transmitter. Here, the transmitter is IR LED whereas the receiver is IR photodiode. The infrared photodiode is responsive to the infrared light that is generated through an infrared LED. The resistance of photo-diode & the change in output voltage is in proportion to the infrared light obtained. This is the IR sensor’s fundamental working principle.


Once the infrared transmitter generates emission, then it arrives at the object & some of the emission will reflect back toward the infrared receiver. The sensor output can be decided by the IR receiver depending on the intensity of the response.

Types of Infrared Sensor

Infrared sensors are classified into two types like active IR sensor and passive IR sensor.

Active IR Sensor

This active infrared sensor includes both the transmitter as well as the receiver. In most of the applications, the light-emitting diode is used as a source. LED is used as a non-imaging infrared sensor whereas the laser diode is used as an imaging infrared sensor.

These sensors work through energy radiation, received & detected through radiation. Further, it can be processed by using the signal processor to fetch the necessary information. The best examples of this active infrared sensor are reflectance and break beam sensor.

Passive IR Sensor

The passive infrared sensor includes detectors only but they don’t include a transmitter. These sensors use an object like a transmitter or IR source. This object emits energy and detects through infrared receivers. After that, a signal processor is used to understand the signal to obtain the required information.

The best examples of this sensor are pyroelectric detector, bolometer, thermocouple-thermopile, etc. These sensors are classified into two types like thermal IR sensor and quantum IR sensor. The thermal IR sensor doesn’t depend on wavelength. The energy source used by these sensors is heated. Thermal detectors are slow with their response and detection time. The quantum IR sensor depends on the wavelength and these sensors include high response and detection time. These sensors need regular cooling for specific measurements.

IR Sensor Circuit Diagram

An infrared sensor circuit is one of the basic and popular sensor modules in an electronic device. This sensor is analogous to human’s visionary senses, which can be used to detect obstacles and it is one of the common applications in real-time. This circuit comprises the following components

  • LM358 IC 2 IR transmitter and receiver pair
  • Resistors of the range of kilo-ohms.
  • Variable resistors.
  • LED (Light Emitting Diode).
Infrared Sensor Circuit Diagram
Infrared Sensor Circuit Diagram

In this project, the transmitter section includes an IR sensor, which transmits continuous IR rays to be received by an IR receiver module. An IR output terminal of the receiver varies depending upon its receiving of IR rays. Since this variation cannot be analyzed as such, therefore this output can be fed to a comparator circuit. Here an operational amplifier (op-amp) of LM 339 is used as a comparator circuit.

When the IR receiver does not receive a signal, the potential at the inverting input goes higher than that non-inverting input of the comparator IC (LM339). Thus the output of the comparator goes low, but the LED does not glow. When the IR receiver module receives a signal to the potential at the inverting input goes low. Thus the output of the comparator (LM 339) goes high and the LED starts glowing.

Resistor R1 (100 ), R2 (10k ), and R3 (330) are used to ensure that a minimum of 10 mA current passes through the IR LED Devices like Photodiode and normal LEDs respectively. Resistor VR2 (preset=5k ) is used to adjust the output terminals. Resistor VR1 (preset=10k ) is used to set the sensitivity of the circuit Diagram. Read more about IR sensors.

IR Sensor Circuit using Transistor

The circuit diagram of the IR sensor using transistors namely obstacle detection using two transistors is shown below. This circuit is mainly used for obstacle detection using an IR LED. So, this circuit can be built with two transistors like NPN and PNP. For NPN, BC547 transistor is used whereas, for PNP, BC557 transistor is used. The pinout of these transistors is the same.

Infrared Sensor Circuit using Transistors
Infrared Sensor Circuit using Transistors

In the above circuit, one infrared LED is always switched on whereas the other infrared LED is allied to the PNP transistor’s base terminal because this IR LED acts as the detector. The required components of this IR sensor circuit include resistors 100 ohms & 200 ohms, BC547 & BC557 transistors, LED, IR LEDs-2. The step by step procedure of how to make the IR sensor circuit includes the following steps.

  • Connect the components as per the circuit diagram using required components
  • Connect one infrared LED to the BC547 transistor’s base terminal
  • Connect an infrared LED to the base terminal of the same transistor.
  • Connect the 100Ω resistor toward the residual pins of the infrared LEDs.
  • Connect the base terminal of the PNP transistor toward the collector terminal of the NPN transistor.
  • Connect the LED & 220Ω resistor as per the connection in the circuit diagram.
  • Once the connection of the circuit is done then gives the power supply to the circuit for testing.

Circuit Working

Once the infrared LED is detected, then the reflected light from the thing will activate a small current that will supply throughout the IR LED detector. This will activate the NPN transistor & the PNP; therefore the LED will switch ON. This circuit is applicable for making different projects like automatic lamps to activate once a person approaches close to the light.

Burglar Alarm Circuit using IR Sensor

This IR burglar alarm circuit is used at entries, doors, etc. This circuit gives a buzzer sound to alert the concerned person whenever someone crosses throughout the IR ray. When the IR rays are not visible to humans, then this circuit works as a hidden safety device.

Burglar Alarm Circuit
Burglar Alarm Circuit using IR Sensor

The required components of this circuit mainly includes NE555IC, resistors R1 & R2 = 10k & 560, D1 (IR photodiode), D2 (IR LED), C1 Capacitor (100nF), S1 (push switch), B1 (Buzzer) & 6v DC Supply.
This circuit can be connected by arranging the infrared LED as well as the infrared sensors on the door opposite to each other. So that IR ray can fall on the sensor properly. Under normal conditions, the infrared ray drops always over the infrared diode & the output condition at pin-3 will stay in the low condition.

This ray will be interrupted once a solid object crosses the ray. When the IR ray smashes, the circuit will activate & the output turns to ON condition. The output condition remains till it retunes by shutting the switch that means, when the interrupt of the ray is detached then an alarm remains ON. To avoid others from deactivating the alarm, the circuit or reset switch must be located distant or out of sight from the infrared sensor. In this circuit, a ‘B1’ buzzer is connected to produce sound with an inbuilt sound and this inbuilt sound can be replaced with an alternative bells otherwise loud siren based on the requirement.

Please refer to this link for; IR Sensor Module Interfacing with Microcontroller – Arduino, PIC.


The advantages of IR sensor include the following

  • It uses less power
  • The detection of motion is possible in the presence or absence of light approximately with equal reliability.
  • They do not need contact with the object for detection
  • There is no data leakage because of the ray direction
  • These sensors are not affected by oxidation & corrosion
  • Noise immunity is very strong


The disadvantages of IR sensor include the following

  • Line of sight is required
  • Range is limited
  • These can be affected by fog, rain, dust, etc
  • Less data transmission rate

IR Sensor Applications

IR sensors are classified into different types depending on the applications. Some of the typical applications of different types of sensors. The speed sensor is used for synchronizing the speed of multiple motors. The temperature sensor is used for industrial temperature control. PIR sensor is used for an automatic door opening system and the Ultrasonic sensor is used for distance measurement.

IR sensors are used in various Sensor based projects and also in various electronic devices which measures the temperature that is discussed below.

Radiation Thermometers

IR sensors are used in radiation thermometers to measure the temperature depend upon the temperature and the material of the object and these thermometers have some of the following features

  • Measurement without direct contact with the object
  • Faster response
  • Easy pattern measurements

Flame Monitors

These types of devices are used for detecting the light emitted from the flames and to monitor how the flames are burning. The Light emitted from flames extend from UV to IR region types. PBS, PbSe, Two-color detector, pyroelectric detector are some of the commonly employed detectors used in flame monitors.

Moisture Analyzers

Moisture analyzers use wavelengths that are absorbed by the moisture in the IR region. Objects are irradiated with light having these wavelengths(1.1 µm, 1.4 µm, 1.9 µm, and 2.7µm) and also with reference wavelengths.

The Lights reflected from the objects depend upon the moisture content and are detected by the analyzer to measure moisture (ratio of reflected light at these wavelengths to the reflected light at reference wavelength). In GaAs PIN photodiodes, Pbs photoconductive detectors are employed in moisture analyzer circuits.

Gas Analyzers

IR sensors are used in gas analyzers that use the absorption characteristics of gases in the IR region. Two types of methods are used to measure the density of gas such as dispersive and nondispersive.

Dispersive: An Emitted light is spectroscopically divided and their absorption characteristics are used to analyze the gas ingredients and the sample quantity.

Nondispersive: It is the most commonly used method and it uses absorption characteristics without dividing the emitted light. Nondispersive types use discrete optical bandpass filters, similar to sunglasses that are used for eye protection to filter out unwanted UV radiation.

This type of configuration is commonly referred to as nondispersive infrared (NDIR) technology. This type of analyzer is used for carbonated drinks, whereas a nondispersive analyzer is used in most of the commercial IR instruments, for automobile exhaust gas fuel leakages.

IR Imaging Devices

IR image device is one of the major applications of IR waves, primarily by virtue of its property that is not visible. It is used for thermal imagers, night vision devices, etc.

For example, Water, rocks, soil, vegetation, and atmosphere, and human tissue all feature emit IR radiation. The Thermal infrared detectors measure these radiations in the IR range and map the spatial temperature distributions of the object/area on an image. Thermal imagers usually composed of an Sb (indium antimonite), Gd Hg (mercury-doped germanium), Hg Cd Te (mercury-cadmium-telluride) sensors.

An electronic detector is cooled to low temperatures using liquid helium or liquid nitrogen.  Then the Cooling the detectors ensure that the radiant energy (photons) recorded by the detectors comes from the terrain and not from the ambient temperature of objects within the scanner itself and IR imaging electronic devices.

The key applications of the infrared sensors mainly include the following.

  • Meteorology
  • Climatology
  • Photo-bio modulation
  • Analysis of Water
  • Gas detectors
  • Testing of Anesthesiology
  • Exploration of Petroleum
  • Safety of Rail

Thus, this is all about the infrared sensor circuit with working and applications. These sensors are used in many sensor-based electronics projects. We believe that you might have got a better understanding of this IR sensor and its working principle. Furthermore, any doubts regarding this article or projects please give your feedback by commenting in the comment section below. Here is a question for you, can the infrared thermometer operate in complete darkness?

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