Ultrasonic range finder (HC-SR04)

Goal

Measure a distance in centimetres with an ultrasonic sensor.

Why it matters

You measure a time of flight: distance = (duration × 340 m/s) / 2, exactly like a radar.

Steps

1. 01Add the ultrasonic sensor (TRIG on 9, ECHO on 10).
2. 02Send a 10 µs pulse on TRIG.
3. 03Measure the echo duration with pulseIn(ECHO, HIGH).
4. 04Convert: cm = duration / 58.

Next tutorials

• Read a push button

  Light the LED only while the button is pressed.

• Toggle button (debounced)

  One press turns on, the next turns off — with no contact bounce.

• Read a potentiometer

  Print the analog value of A0 on the serial monitor.

• Convert to volts (map & float)

  Turn the ADC's 0–1023 into a 0.00–5.00 V reading.