The Ultrasonic Distance Sensor HC-SR04

In order to measure the distance of the colored paper sheet from the sensors we use the HC-SR04 ultra-sonic distance sensor.

As can be seen from the photo, the modules has 4 connections:

• Vcc, which is 5V
• Gnd
• Trig
• Echo

The module is triggered with a 10us TTL trigger pulse. It then sends an 8 cycle sonic burst of 40 kHz and tries to detect the echo. The module sends an echo pulse whose length is proportional to the time the sound signals takes to the target and back.

These are the connection we make:

Vcc	5V
Trig	gpio 23
Echo	gpio 24 via the level converter
Gnd	Gnd

Here is a Python test program demonstrating the readout:

https://afnog.iotworkshop.africa/pub/AFNOG/Ultra-sonicSensor/hc-sr04.py.txt

-- Uli Raich - 2018-02-08

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