Infrared Sensor Working Principle

Is everything visible around you? Are you only grabbing benefits from the visible things only? No. Many invisible phenomena exist on our Earth, with which we are accomplishing our desires! Such a phenomenon is the infrared ray. The wavelength of the ray typically ranges from 700 nm to 1 mm. Infrared or IR sensors are mostly used sensors that we use in TV remotes to obstacle-detecting robots because of their simplicity and versatile working capability.

Table of Contents

• What is an Infrared (IR) Sensor?
• Working Principle: How it works?
• Explanation of IR Sensor's Circuit Diagram
• Types of IR sensors
• IR Sensor Applications
• Limitations of IR sensors

What is an Infrared (IR) Sensor?

An electronic device that emits and detects infrared radiation to sense objects in its surrounding environment is an infrared (IR) sensor, which powers industrial automation systems. An electronic device that emits and detects infrared radiation to sense objects in its surrounding environment is an infrared (IR) sensor, which powers industrial automation systems. These electronic gadgets receive or produce infrared radiation, a type of electromagnetic energy imperceptible to the human eye, allowing machines to see and engage with their surroundings in manners that emulate biological senses.

Working Principle: How it works?

For a deep dive into the infrared sensors, their mechanism of working should be studied. Here, two key components are involved in the operation of an infrared sensor: an IR emitter and an IR detector.

The Infrared Emitter: It’s the origin of Invisible Light. An Infrared Light Emitting Diode (IR LED) is the most widely used IR emitter. An IR LED uses infrared wavelengths to transform electrical energy into light, just like a conventional LED. These LEDs are made especially to emit infrared light, which is subsequently focused on a target or other area of interest. In more specializeds where highly focused beams are needed, infrared lasers are also employed.

IR Detector: It senses invisible things. The IR photodiode is the main part in charge of sensing infrared radiation. A semiconductor device known as an infrared photodiode changes its electrical characteristics, particularly its output voltage and resistance, when it is subjected to infrared light. The intensity of the incident infrared light directly correlates with this shift. Phototransistors are additional detectors that provide greater amplification and sensitivity.

Basic principle of an IR sensor

When an infrared transmitter and receiver are used together, the wavelengths of the transmitter and receiver must match. In this case, an IR LED serves as the transmitter and an IR photodiode as the receiver. The infrared light produced by an infrared LED causes the infrared photodiode to react. The amount of infrared light produced is proportional to the photo-diode's resistance and the output voltage variation. This is the basic idea behind how an infrared sensor operates. When the emission from the infrared transmitter reaches the item, some of it will reflect back to the infrared receiver. The IR receiver can determine the sensor output based on the response's intensity. 

Steps are at a glance:

•  The IR LED emits infrared light.
•  If there’s a reflective object in front, IR rays reflect back.
• The photodiode senses the reflected IR light.
• The amount of light received affects the current through the photodiode.
• This current is converted into a voltage and sent to an Op-Amp comparator.
•  If the voltage is above a set threshold, the sensor outputs a HIGH signal (usually 5V), indicating the presence of an object.

Explanation of IR Sensor's Circuit Diagram:

The IR sensor serves its purpose by developing a circuit that includes major components: infrared LED, photodiode, variable resistor/potentiometer, and capacitors. Infrared light is continuously emitted by the IR LED. This light is reflected back at the photodiode by an object positioned in front of it.

Circuit Diagram of IR Sensor (Source: circuitdigest.com)

The IR sensor circuit diagram shows the connections. The photo diode is placed in reverse bias, and the inverting end of LM358 (PIN 2) is linked to the variable resistor to modify the sensor's sensitivity. The non-inverting end (PIN 3) is linked to the junction of a photodiode and resistor. When we turn on the circuit, there is no IR radiation towards the photodiode, and the comparator's output is LOW. When we place a non-black object in front of an IR pair, the IR emitted by the IR LED is reflected and absorbed by the photodiode. When reflected IR falls on the photodiode, the voltage across the photodiode decreases while the voltage across series resistor R2 increases. When the voltage at Resistor R2 (attached to the non-inverting end of the comparator) exceeds the voltage at the inverting end, the output becomes HIGH and the LED turns on. The voltage at the inverting end, commonly known as the threshold voltage, can be adjusted by moving the variable resistor knob. The higher the voltage at the inverting end (-), the less sensitive the sensor; the lower the value at the inverting end, the more sensitive the sensor.

Types of IR sensors:

Active Infrared Sensors: These sensors combine an infrared emitter (transmitter) and a receiver (receiver) into one unit or in independent parts that face one another. Emitting infrared light and then detecting the reflected or interrupted radiation is how they work.

Reflective infrared sensors: These sensors have the emitter and detector positioned next to each other. The photodiode detects the infrared light that the LED emits after it bounces off an object. These are frequently utilized in line following, robot obstacle avoidance, and proximity sensing.

Transmissive infrared sensors: It’s also known as photo-interrupters, have a gap between the emitter and detector, which are oriented facing one another. The detector's output changes when an object disrupts the infrared beam as it travels through this gap. Limit switches, rotating encoders, and object counting are a few examples of applications.

Passive infrared sensors:  This kind of sensors don't release any infrared radiation, in contrast to active sensors. Rather, they are limited to detecting infrared light that is naturally generated by objects inside their field of vision. Based on variations in the infrared energy patterns in their surroundings, PIR sensors are mostly employed to identify motion or the presence of warm bodies (such as people or animals).

Additional categories for passive infrared sensors include:

Thermal Infrared Sensors: These sensors use heat from infrared radiation as a source. Pyroelectric detectors, bolometers, and thermocouples are a few examples. Although they can function at ambient temperature, they often respond more slowly.

Quantum infrared sensors: These sensors work by transforming incident photons into electrons using the photoelectric effect. They have quicker reaction times and better detection performance, but they frequently need cooling to cut down on noise.

IR Sensor Applications:

Consumer electronics: Infrared sensors are frequently used in remote controls.

Motion Detectors for Security Systems: PIR sensors pick up movement and body heat. Automatic door openers uses active infrared to detect human presence.

Robotics: Infrared sensors can distinguish between black lines on white surfaces. Robots employ infrared sensors to identify presence of obstacles.

Industrial Automation: Conveyor belts are detected by IR sensors and utilized in counting section. These sensors also perform position sensing. They determine where machine components are located.

Medical Equipment: Devices like pulse oximeters test blood oxygen levels using infrared and red LEDs.

Advantages of using IR sensors:

Non-Contact Detection: Prevents contamination or wear and tear by enabling detection without physical contact.

Low Power Consumption: Because many infrared sensors use little energy, they can be used with devices that run on batteries.

Cost-effective and Simple Design: Simple infrared sensor modules are affordable and simple to include into circuits.

Quick Response Time: Active infrared sensors are able to give prompt feedback on detections.

Limitations of IR sensors:

Requirement of line of sight: The majority of active infrared sensors need a direct line of sight between the emitter, the object, and the detector. The signal may be blocked by obstructions.

Restricted Range: In general, infrared sensors have a short to medium effective range, particularly when contrasted with radar or ultrasonic sensors.

Environmental Sensitivity: Ambient light, particularly intense sunlight, fog, smoke, dust, and extremely high or low temperatures can all impair performance by interfering with the transmission or detection of infrared signals.

Color Insensitivity: Infrared sensors detect variations in infrared energy, which has nothing to do with the colors of visible light.

Problems with Transparency: IR light can travel through some transparent materials, such as water or clear glass, making detection challenging.

Robustness: Generally speaking, robustness is impervious to electrical noise.

Modern electronics rely heavily on infrared sensors because of their affordability, ease of use, and adaptability. IR sensors provide a dependable solution for proximity and motion detection, whether you're building a basic robot that avoids obstacles or automating a security system. They do have certain drawbacks, especially with regard to range and susceptibility to outside interference, but these may be mostly addressed with appropriate circuit design and modulation methods. Their wide range of uses in consumer electronics, industrial automation, robotics, and medical equipment show how essential infrared sensors are to the development of intelligent systems. Gaining insight into the inner workings of infrared sensors not only improves your understanding of electronics but also leads to a plethora of professional and do-it-yourself automation and control system opportunities.