For sensing distance to obstacles, an HC-SR04 sensor module has been used. It has an ultrasonic transducer which generates the ultra sonic waves, an ultra sonic receiver and control circuitry built on a small PCB.
For interfacing with microcontroller it provides two lines namely TRIGGER and ECHO. The trigger pin is an input pin, the MCU sends a 10uS high pulse on this line to tell the HC-SR04 to start a taking a measurement.
As soon as the HC-SR04 receives this pulse it sends out ultrasonic waves and waits for it to goto the obstacle and come back to the sensor. The sensor then emits a pulse on the ECHO line whose width is equal to this time. By simple calculation we can find the distance to obstacle.
Three such such sensors are used in this project to find obstacle in front, left and right of the user.
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