HC-SR04 ultrasonic range sensor
This sensor uses a simple pulse echo to compute the distance to an object. It simply emits a high frequency 'ping' and measures the time taken for the echo to return. The distance to an object is then calculated using a simple formula.
To operate the sensor, the Vcc and Gnd pins should be connected to 5V and
ground respectively. The remining pins, Trig and Echo, should be connected
to digital pins on the Arduino. A pulse is sent to the Trig pin by raising
the pin to 5V for a short period such as 10 milliseconds. The echo is
received and processed automatically by the sensor which delivers a pulse
back on the Echo pin. The duration of the echo pulse indicates the
distance from the object. The pulse can be read using the Arduino pulseIn()
function. The distance in centimetres can be calculated using the formula:
Datasheet