HC-SR04 Ultrasonic Sensor Module

HC-SR04 Ultrasonic Sensor Module

This sensor is popular among hobbyists and makers for several good reasons. It uses very little power, making it perfect for battery-powered projects. It’s also affordable—you can usually find these sensors for just a few dollars. Best of all, it’s super easy to connect to an Arduino or other microcontrollers.

Specifications:

• Operating Voltage:   DC 5V
• Operating Current:   15mA
• Operating Frequency:   40KHz
• Max Range:   4m
• Min Range:   2cm
• Ranging Accuracy:   3mm
• Measuring Angle:   15 degree
• Trigger Input Signal:   10µS TTL pulse
• Dimension:  45 x 20 x 15mm

How Does HC-SR04 Ultrasonic Sensor Work?

It all starts, when a pulse of at least 10µS (10 microseconds) in duration is applied to the Trigger pin. In response to that the HC-SR04 Ultrasonic Sensor transmits a sonic burst of eight pulses at 40 KHz. This 8-pulse pattern makes the ultrasonic signature from the device unique, allowing the receiver to differentiate the transmitted pattern from the ambient ultrasonic noise.

The eight ultrasonic pulses travel through the air away from the transmitter. Meanwhile the Echo pin goes HIGH to start forming the beginning of the echo-back signal.

In case, If those pulses are not reflected back then the Echo signal will timeout after 38 mS (38 milliseconds) and return low. Thus a 38 mS pulse indicates no obstruction within the range of the sensor.

If those pulses are reflected back the Echo pin goes low as soon as the signal is received. This produces a pulse whose width varies between 150 µS to 25 mS, depending upon the time it took for the signal to be received.

The width of the received pulse is then used to calculate the distance to the reflected object. This can be worked out using simple distance-speed-time equation, we learned in High school. In case you forgot, an easy way to remember the distance, speed and time equations is to put the letters into a triangle.

Lets take an example to make it more clear. Suppose we have an object in front of the sensor at an unknown distance and we received a pulse of width 500 µS on the Echo pin. Now lets calculate how far the object from the sensor is. We will use the below equation.

Distance = Speed x Time

Here, we have the value of Time i.e. 500 µs and we know the speed. What speed do we have The speed of sound, of course! Its 340 m/s. We have to convert the speed of sound into cm/µs in order to calculate the distance. A quick Google search for ‘speed of sound in centimeters per microsecond’ will say that it is 0.034 cm/µs. You could do the math, but searching it is easier. Anyway, with that information, we can calculate the distance!

Distance = 0.034 cm/µs x 500 µs

But this is not done! Remember that the pulse indicates the time it took for the signal to be sent out and reflected back so to get the distance so, you’ll need to divide your result in half.

Distance = (0.034 cm/µs x 500 µs) / 2

Distance = 8.5 cm

So, now we know that the object is 8.5 centimeters away from the sensor.

Package Includes:

• 1x HC-SR04 Ultrasonic Sensor Module

Documents:

• HC-SR04 Ultrasonic Sensor Datasheet

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