Sonar Sensor HC-SR04

You must have heard about the process of measuring the depth of the sea by sound navigation technique. The process is known as SOund NAvigation and Ranging (SONAR). Using the same principle, we have a couple of sonar sensor modules available for daily life projects. HC-SR04, being the most popular one, is widely used. Let's try to dive into it.

Why?

◉ Distance measurement: The exact distance of an object can be figured out by using this sensor. This includes Level Monitoring in tanks, liquid, trash, bottle, etc.

◉ Security installations: Intruders can be detected in the preset range using an ultrasound sensor.

◉ Advanced applications: Practical applications of ultrasound sensors in diversified fields. Check the following links to know more;

* https://www.migatron.com/ultrasonic-detections-and-control-applications/

* https://www.maxbotix.com/articles/ultrasonic-sensor-applications.htm

* https://www.microcontrollertips.com/principle-applications-limitations-ultrasonic-sensors-faq/

* https://www.pepperl-fuchs.com/global/en/24854.htm

Kinds of Ultrasound sensor:

There are two kinds of ultrasound sensor;

◉ Proximity detection: An object passing within the preset range will be detected and generate an output signal. The detect point is independent of target size, material, or reflectivity.

◉ Ranging measurement: Precise distance(s) of an object moving to and from the sensor are measured via time intervals between transmitted and reflected bursts of ultrasonic sound. Distance change is continuously calculated and outputted.

Working Principle:

By the name, it is easily understandable that this sensor uses ultrasound for its purpose. But why ultrasound? Can you take a guess? There are many more waves like microwaves and others. Then why ultrasound?

Sound with a frequency greater than 20KHz is called ultrasound. The physical properties of ultrasound are the same as normal sound but humans can't hear it. There are basically a couple of reasons why ultrasound is used in sonar.

✔ Ultrasound, having a high frequency and short wavelength, can penetrate to a long-distance (in water too).

✔ It can't be confused with other sounds. Therefore, the receiver can pick very easily.

Now the procedure goes like this, the module produces ultrasound using a piezoelectric sensor. The sound keeps traveling and upon reflection to an object, the reflected sound is received by the receiver placed in the module. The time required to send the signal and receive the is calculated by the crystal oscillator. Then the distance is calculated by the equation;

Distance = 0.5 * Time * Speed of sound

The velocity of the sound is temperature-dependent. At 20 °C (68 °F), the speed in air is 343 m/s (1235 km/h; 1125 ft/s; 767 mph)

Module Pinout & Functioning:

This module has 4 interfacing pins; Vcc, Trig, Echo & GND respectively.

Pin No.	Pin Name	Description
1	Vcc	Input power pin. Typically 5V
2	Trigger	This input pin has to be kept high for 10us to initialize measurement by sending US wave
3	Echo	This is the output pin. It remains high for a time period equal to the time, taken for the US wave to return back to the sensor
4	Ground	Connected to the system ground