Input devices

For this week, we decide to test the ultrasonic sensor HC-SR04. HC-SR04

HC-SR04 sensor


How it works ?

To trigger a measurement, a “high” pulse (5 V) of at least 10 μs must be presented on the “Trig” input.

The sensor then emits a series of 8 ultrasonic pulses at 40 kHz and then waits for the reflected signal.

When this is detected, it sends a signal “high” on the output “Echo”, whose duration is proportional to the measured distance.


We connected Julie’s board to the FTDI to power our sensor and then we started measuring with the oscilloscope what was going on.


This is what we observed on the oscilloscope. We can clearly see a little delay between the 2 signals. It’s the time the signal takes to come back to the sensor.