Introduction to Proximity Sensor

The proximity sensor measures the distance between itself and the target object. The sensor takes distance as the input and provides an output which can be in the form of analog voltage, digital data, or a pulse (PWM). The proximity sensor is widely employed in electrical engineering and electronics industries.

Types of proximity sensors

Ultrasonic proximity sensor

This sensor uses the piezoelectric transducer to generate a sound (having frequency above 20kHz) and then receives the sounds for echoes. It works perfectly for distances > 1m and is recommended for liquids and transparent objects. Compare to infrared sensors, it is larger in size. However, it is unaffected by sunlight and other light sources.

Infrared proximity sensor

It uses a beam of infrared light from an LED source. After striking target, the Light returns back and is detected by the photodiode. The entire construction involves complex electronic components which detect and calculate the distance.

Schematic symbol


Practical Applications

  1. Your mobile phone uses a proximity sensor which switches the display when your ear or hand is brought closer.
  2. In small electronics, it is used to prevent collisions with obstacles.
  3. It is used in Electrical Engineering industries to monitor the industrial processes.

HC – SR04 Ultrasonic Distance Measuring Sensor


HC- SR04 Ultrasonic distance measuring sensor (shown above) is an economically available model which can be used with Arduino board. Hobbyists and electronics lovers can employ it in their projects.

Lets understand working of HC – SR04 from a video tutorial:

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