Pulse duration is the full time between the sensor outputting an ultrasonic pulse, and the return pulse being detected by the sensor receiver.

Once a return pulse has been located ECHO is set “high” (5V) for the duration of that pulse.

The sensor detects these return waves and measures the time between the trigger and returned pulse, and then sends a 5V signal on the ECHO pin.ĮCHO will be “low” (0V) until the sensor is triggered when it receives the echo pulse. The pulse waves bounce off any nearby objects and some are reflected back to the sensor. We power the module using Vcc, ground it using GND, and use our Raspberry Pi to send an input signal to TRIG, which triggers the sensor to send an ultrasonic pulse. The HC-SR04 Ultrasonic sensor we’ll be using in this tutorial for the Raspberry Pi has four pins: ground (GND), Echo Pulse Output (ECHO), Trigger Pulse Input (TRIG), and 5V Supply (Vcc). This time can subsequently be used, along with some clever math, to calculate the distance between the sensor and the reflecting object. That return signal is then processed by the control circuit to calculate the time difference between the signal being transmitted and received. Some of that ultrasonic noise is reflected and detected by the receiver on the sensor. The transmitters emit a high frequency ultrasonic sound, which bounce off any nearby solid objects. You could of course use Acoustic sound for this purpose, but you would have a noisy robot, beeping every few seconds.Ī basic ultrasonic sensor consists of one or more ultrasonic transmitters (basically speakers), a receiver, and a control circuit. Ultrasound is mainly used because it’s inaudible to the human ear and is relatively accurate within short distances. Ultrasonic sensors are designed to sense object proximity or range using ultrasound reflection, similar to radar, to calculate the time it takes to reflect ultrasound waves between the sensor and a solid object. Very low frequency sound below Acoustic is defined as “Infrasound”, with high frequency sounds above, called “Ultrasound”. Only some of the sound spectrum (the range of sound wave frequencies) is audible to the human ear, defined as the “Acoustic” range. Sound consists of oscillating waves through a medium (such as air) with the pitch being determined by the closeness of those waves to each other, defined as the frequency. The HC-SR04 ultrasonic range finder is very simple to use, however the signal it outputs needs to be converted from 5V to 3.3V so as not to damage our Raspberry Pi! We'll introduce some Physics along with Electronics in this tutorial in order to explain each step! In previous tutorials we've outlined temperature sensing, PIR motion controllers and buttons and switches, all of which can plug directly into the Raspberry Pi's GPIO ports.

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