Updated: July 9th, 2018

IoT infrared sensors are commonly used to create smart and connected products which make use of sensors such as proximity sensors, motor control, and level sensors. These sensors are utilized by a number of industries, ranging from military to consumer goods products. Infrared sensors can be used to create a range of smart products including heart rate and fitness monitors, security alarm circuits and smart toys. This article explores different infrared sensors used in smart products. 

Infrared Technology

Infrared light consists of electromagnetic radiation that has longer wavelengths than those of visible light. Infrared devices always contain the following two elements: a light emitter and a light detector. An infrared emitter is a light emitting diode (LED) that emits invisible light within the range of the infrared spectrum.  A light detector, or photodetector, contains semiconductor material which converts light signals into voltage or current that can be measured and is proportional to the amount of the light absorbed by the semiconductor material. These two elements can be combined in various ways to create infrared sensors, including the following sensors which are commonly used in the IoT industry.  

iot infrared sensors - wavelengths
The Electromagnetic Spectrum. Image credit: astronomersgroup

Proximity Sensor

The proximity sensor detects infrared light which hits an object and is then reflected back towards the light detector. As the object moves closer to the sensor, the reflected light hitting the detector will be stronger than when the object is far away. If the intensity of the reflected light passes a certain threshold, the circuit changes its state and the processing unit connected to the sensor will then execute an action e.g., prevent a vehicle from hitting a wall.

iot infrared sensors - principles
The operation of an infrared sensor. Image credit: education.rec.ri.cmu.edu

Infrared Encoder

The infrared encoder is an electromechanical device where the light emitter and the photodetector are used in conjunction with a slotted disc in order to determine how far a rotational mechanism has turned. The slotted disc is connected to a motor so that the disc turns with the motor at the same rate and enables the light to pass through the slots, creating pulses of light that are picked up by the detector. The photodetector is connected to a microprocessor that counts the number of pulses that correlates to the slots that are passed between the emitter and the detector. The number of slots is correlated with the motor movement enabling the microprocessor to calculate and control the motor movements.     

Liquid Level Sensor

The liquid level sensor changes its output signal when it senses the presence or absence of fluids. When infrared light hits the fluid, some of the light scatters (changes its direction) and as a result the signal picked up by the detector is weaker than when no fluid is present. The liquid level sensor can also detect when the fluid level passes a predefined threshold.

iot infrared sensors - liquid level
Liquid level sensor. Image credit: omega.com

Heartbeat Light Sensor

The heartbeat light sensor measures the number of times the heart beats per minute (BPM). The heartbeat pulse causes a variation in blood flow to the different regions of the body and these variations are correlated to the variations in light that reflect off the body and the amount of light absorbed by the photodetector. The microprocessor analyzes the results and calculates the heart rate.    

Advantages of Infrared Sensors for IoT

As can be seen, there are some major benefits of using sensors that are based on infrared technology to create smart products. It is relatively simple and cheap to operate requiring low levels of power and it can be applied to diverse solutions and sensor applications. There are a few disadvantages that need to be considered when using infrared technology:  ambient light and dust surrounding the sensor can influence the accuracy of the results and the light source needs to be in direct line with the detector at all times. When choosing infrared sensors to build smart products, it’s important to ensure that the sensor meets the requirements of the product and can function within the environmental constraints of the smart product.