Saturday, February 24, 2024

Understanding IR Sensors and IR LEDs: Functions, Differences, and Applications

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This article is a comprehensive overview of both IR sensors and IR LEDs, including their functions, components, working principles, applications, and differences.

An Infrared light-emitting diode (IR LED) is a special-purpose LED that emits infrared rays ranging from 700 nm to 1 mm wavelength. Different IR LEDs may produce infrared light of differing wavelengths, just like other LEDs produce light of different colors.

IR sensor is a device that uses infrared technology to detect objects or changes in the environment. IR sensors can detect a wide range of physical properties such as temperature, motion, and proximity.

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IR LEDs are usually made of gallium arsenide or aluminum gallium arsenide. In complement with IR receivers, these are commonly used as sensors.

The appearance of an IR LED is the same as a common LED. Since the human eye cannot see infrared radiation, it is not possible for a person to identify if an IR LED is working. A camera on a cell phone camera solves this problem. The IR rays from the IR LED in the circuit are shown in the camera.

Pin Diagram of IR LED

IR LED Pins
IR LED Pins

An IR LED is a type of diode or simple semiconductor. Electric current is allowed to flow in only one direction in diodes. As the current flows, electrons fall from one part of the diode into holes on another part.

In order to fall into these holes, the electrons must shed energy in the form of photons, which produce light.

It is necessary to modulate the emission from the IR diode to use it in the electronic application to prevent spurious triggering. Modulation makes the signal from IR LED stand out above the noise.

Infrared diodes have a package that is opaque to visible light but transparent to infrared. The massive use of IR LEDs in remote controls and safety alarm systems has drastically reduced the pricing of IR diodes in the market.

IR Sensor

An IR sensor is an electronic device that detects IR radiation falling on it. Proximity sensors (used in touchscreen phones and edge-avoiding robots), contrast sensors (used in line following robots), and obstruction counters/sensors (used for counting goods and in burglar alarms) are some applications involving IR sensors.

IR Sensor Working Principle

An IR sensor consists of two parts, the emitter circuit, and the receiver circuit. This is collectively known as a photo-coupler or an optocoupler.

The emitter is an IR LED and the detector is an IR photodiode. The IR photodiode is sensitive to the IR light emitted by an IR LED. The photodiode’s resistance and output voltage change in proportion to the IR light received. This is the underlying working principle of the IR sensor.

The type of incidence can be direct incidence or indirect incidence. In direct incidence, the IR LED is placed in front of a photodiode with no obstacle.

In indirect incidence, both the diodes are placed side by side with an opaque object in front of the sensor. The light from the IR LED hits the opaque surface and reflects back to the photodiode.

IR Sensor Working Principle
IR Sensor Working Principle

IR Receiver LED and IR Transmitter LED

An IR receiver LED and an IR transmitter LED are both types of light-emitting diodes (LEDs) that are used in infrared (IR) communication.

An IR receiver LED is a device that detects infrared signals from remote controls and other IR sources. It is typically a small, clear, or translucent device that is sensitive to IR light in a specific frequency range.

When an IR signal is detected, the IR receiver LED will emit a small amount of visible light, which can be used to confirm that a signal has been received.

An IR transmitter LED, on the other hand, is a device that emits infrared light in order to send signals to other devices. It is typically a small, clear, or translucent device that emits IR light in a specific frequency range. IR transmitter LEDs are commonly used in remote controls and other IR signaling devices.

In summary, the IR receiver LED detects the IR signal from the remote, and the IR transmitter LED emits the IR signal from the remote.

IR Sensor Module

IR Sensor Module with Circuit
IR Sensor Module with Circuit

An IR sensor module is a device that contains an IR receiver LED and other components that are used to detect and process IR signals. It typically includes an IR receiver LED, a signal amplifier, and a demodulator circuit.

The IR receiver LED is used to detect IR signals, while the signal amplifier and demodulator circuit are used to amplify and process the received signal, respectively.

IR sensor modules are widely used in various electronic applications such as remote control, motion detection, proximity sensing, and more. They are commonly used in consumer electronics, robotics, and automation systems.

IR sensor modules come in various forms such as simple IR receiver modules and complex IR sensor modules with additional features such as signal processing and signal filtering. Some IR sensor modules also provide an output in a digital format that can be read by a microcontroller or microprocessor.

IR sensors find a wide variety of applications in various fields. Let’s take a look at a few of them.

IR Sensor Types

There are several types of IR sensors, each with different characteristics and applications. Some common types include:

  1. Passive Infrared (PIR) Sensor: PIR sensors are used to detect motion by sensing changes in infrared radiation. They are commonly used in security systems, lighting control, and automatic doors.
  2. Reflective IR Sensor: Reflective IR sensors use infrared LED to emit infrared light and a phototransistor to detect the reflected light from an object. They are used to measure distance and detect proximity.
  3. Transmissive IR Sensor: Transmissive IR sensors use infrared LED to emit infrared light and a phototransistor to detect the light that passes through an object. They are used to measure distance and detect proximity.
  4. IR proximity Sensor: IR proximity sensors are used to detect the presence of an object without making physical contact. They are commonly used in mobile devices, robotics, and automation systems.
  5. IR temperature Sensor: These can measure the temperature of an object by detecting the infrared radiation emitted by it. They are used in industrial, HVAC, and medical applications.
  6. IR spectroscopy Sensor: These can use infrared radiation to analyze the properties of a substance. They are used in chemical analysis, medical diagnosis, and environmental monitoring.
  7. IR Imaging sensor: These sensors use infrared radiation to create images, they are used in thermal imaging, night vision, and surveillance cameras.

IR Sensor FAQs

Here are some frequently asked questions about IR sensors and their answers:

Q: What is the working principle of an IR sensor?

A: IR sensors work by detecting infrared radiation emitted by objects in the environment. They typically use a photodiode or a phototransistor to detect the IR radiation and convert it into an electrical signal that can be processed and analyzed.

Q: What is the range of an IR sensor?

A: The range of an IR sensor depends on its type and the specific application. Some IR sensors can detect objects at a distance of several meters, while others are designed for short-range detection of a few centimeters. The sensor has a maximum range of around 40-50 cm indoors and around 15-20 cm outdoors

Q: What are the advantages of IR sensors?

A: IR sensors have many advantages, including high accuracy, non-contact operation, and immunity to electromagnetic interference. They are also widely available and relatively inexpensive.

Q: What are the applications of IR sensors?

A: IR sensors are used in a wide range of applications, including security systems, motion detection, temperature measurement, proximity sensing, and many more.

Q: How do I choose the right IR sensor for my application?

A: Choosing the right IR sensor depends on your specific application and the parameters you need to measure. Consider factors such as the range, sensitivity, accuracy, and cost of the sensor, and consult with sensor manufacturers or experts in the field for guidance.

Q: How to interface the IR sensor with a microcontroller?

A: There are different ways to interface an IR sensor with a microcontroller, it depends on the type of IR sensor and the microcontroller you are using. Typically, the IR sensor output is connected to an input pin of the microcontroller, and the microcontroller reads the output and processes it accordingly.

Q: Can IR sensors detect through walls or other obstacles?

A: It depends on the type of sensor and the specific application. Some IR sensors are designed for long-range detection and may be able to detect objects through walls or other obstacles, while others are designed for short-range detection and may not be able to detect objects through obstacles.

Q: How do IR sensors work in bright sunlight or other bright environments?

A: IR sensors may be affected by bright sunlight or other bright environments. To reduce the effects of ambient light, some sensors use filters or other techniques to block out unwanted light, while others use specialized sensors that are less sensitive to bright environments.

Q: Can IR sensors detect transparent objects?

A: Some IR sensors, like reflective IR sensors, may not be able to detect transparent objects as they rely on the reflection of infrared light. However, other types of IR sensors, like transmissive IR sensors, are designed specifically for transparent object detection, by sensing infrared light that passes through an object.

Q: Can IR sensors work in extreme temperatures?

A: Many IR sensors are designed to operate within a specific temperature range, and may not work properly outside of this range. Some IR sensors are specifically designed for use in extreme temperatures and can operate in a wide range of temperatures.

Q: Are IR sensors affected by humidity?

A: Some IR sensors may be affected by humidity, as humidity can change the properties of the infrared radiation they detect. To reduce the effects of humidity, some sensors use special materials or coatings that are less affected by humidity, while others use specialized sensors that are less sensitive to humidity.

Q: Can IR sensors detect color?

A: IR sensors typically detect infrared radiation, which is outside the visible spectrum and is not associated with color. Some IR sensors are specifically designed to detect specific wavelengths of infrared radiation, but they don’t detect color.

IR LED Sensor based Projects

1. Proximity Sensors

Proximity sensors employ the reflective indirect incidence principle. The photodiode receives the radiation emitted by the IR LED once reflected back by the object. The closer the object, the higher will be the intensity of the incident radiation on the photodiode. This intensity is converted to voltage to determine the distance.

Proximity sensors find use in touchscreen phones, among other devices. The display is disabled during calls so that even if the cheek makes contact with the touchscreen, there is no effect.

2. Line Follower Robots

In line following robots, IR sensors detect the color of the surface underneath it and send a signal to the microcontroller or the main circuit which then takes decisions according to the algorithm set by the creator of the bot.

Line followers employ reflective or non-reflective indirect incidence. The IR is reflected back to the module from the white surface around the black line. But IR radiation is absorbed completely by black color. There is no reflection of the IR radiation going back to the sensor module in black color.

The project is available at the line follower robot

3. Item Counter

Item counter is implemented on the basis of direct incidence of radiation on the photodiode. Whenever an item obstructs the invisible line of IR radiation, the value of a stored variable in a computer/microcontroller is incremented.

This is indicated by LEDs, seven-segment displays, and LCDs. Monitoring systems of large factories use these counters for counting products on conveyor belts.

The project is available at Infrared Object Counter

4. Burglar Alarm

Direct incidence of radiation on the photodiode is applicable in the burglar alarm circuit. The IR LED is fit on one side of the door frame and the photodiode on the other. The IR radiation emitted by the IR LED falls on the photodiode directly under normal circumstances. As soon as a person obstructs the IR path and triggers an alarm.

This mechanism is used extensively in security systems and is replicated on a smaller scale for smaller objects, such as exhibits in an exhibition.

The project is available at Infrared Burglar Alarm

5. IR Music Transmitter and Receiver

Using IR transmitter/receiver & music generator, audio musical notes can be generated and heard up to a distance of 10 meters. The IR music transmitter works off a 9V battery, while the IR music receiver works off regulated 9V to 12V.

The project is available at IR Music Transmitter and Receiver

6. Playing With IR Sensors

There are various applications of IR sensors such as TV remote controllers, burglar alarms, and object counters. Here we have used infrared LEDs to make an object-detection circuit and also a proximity sensor for path-tracking robots.

The project is available at Playing With IR Sensors

7. Wireless Security System Using PIR Sensors

This project demonstrates a wireless security system in which four pyroelectric infrared (PIR) motion sensors are placed on four sides – front, back, left, and right of the area to be covered. It detects motion from any side and turns on the audio-visual alarm. It also displays the side where the motion (intruder) is detected.

The project is available at Wireless Security System

8. Object & Proximity Infrared Detector

Here we have used IR sensors to make an object detection circuit and a proximity sensor for path-tracking robots.

The Project is available at Object & Proximity Infrared Detector

Difference Between IR Sensor and IR LED

Beginners most of the get confused in between these two names. Let’s solve this confusion-

IR Sensor and IR LED are two distinct components used in electronics, particularly in applications involving infrared technology. While they both deal with infrared radiation, they serve different purposes and have different functionalities. Here’s a breakdown of the key differences between IR sensors and IR LEDs:

IR Sensor:

  1. Function:
    • IR sensors are used to detect infrared radiation emitted or reflected by objects. They are capable of sensing changes in IR radiation, which allows them to detect motion, proximity, temperature, and more.
  2. Components:
    • An IR sensor typically consists of an IR emitter (usually an IR LED) and an IR receiver (usually a photodiode or phototransistor). The receiver detects the IR radiation and converts it into an electrical signal that can be processed.
  3. Working Principle:
    • IR sensors work based on the principle that certain materials emit or reflect IR radiation when subjected to changes in temperature or when an object approaches.
  4. Applications:
    • IR sensors are used in a wide range of applications, including security systems, automatic doors, motion detection, temperature measurement, touchless switches, and more.

IR LED:

  1. Function:
    • IR LEDs are light-emitting diodes that emit infrared light when an electric current passes through them. This emitted IR light is not visible to the human eye but can be detected by IR sensors and cameras sensitive to IR radiation.
  2. Components:
    • An IR LED is a semiconductor device that emits infrared light when current flows through it.
  3. Working Principle:
    • IR LEDs work on the same principle as regular LEDs, where the flow of electric current through the semiconductor material causes electrons to move and release energy in the form of photons (light). In the case of IR LEDs, this energy is released in the form of infrared light.
  4. Applications:
    • IR LEDs are used in various applications where the emitted IR radiation is used for communication, remote control systems (like TV remotes), security systems, night vision cameras, optical sensors, and more.

In summary, the main difference between an IR sensor and an IR LED lies in their functions and roles within electronic systems. IR sensors detect and respond to IR radiation, allowing them to sense various parameters like temperature and motion.

On the other hand, IR LEDs emit IR radiation, which can be detected by IR sensors or used for communication and signaling purposes.


This article was first published on 30 October 2017 and recently updated on August 2023.

13 COMMENTS

    • In this case the circuit is checking that the sensor is detecting ir-light. If the light stream is interrupted, the normally high signal from said sensor will be low. This is an extremely common application for these components.

  1. I have seen quite a few questions about testing an IR LED. Since you cannot see any light, how do you know it is working? Well, I had the same question.

    I found a very simple way to do this that costs absolutely nothing if your PC has a built-in camera. To make it easier to see, turn off any extra lights in the room. Turn on the camera in Settings or the Control Panel depending on your computer type. Turn on your LED circuit, and point the LED at the camera. If the LEDs are working, you will see a purple glow around them on the PC screen, indicating the LEDs are on. To confirm this, turn off your circuit and look at the LEDs again. There will be no purple glow.

  2. Folks,

    I am looking for someone with experience with IR components to help define, design and build a distance measuring device for an actuator control application. Can anyone provide any references for a competent engineer interested in sub-contracting?

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