The HC-SR04 ultrasonic sensor uses sonar to determine distance to an object - just like bats or dolphins do. Ultrasonic ranging module HC-SR04 provides 2cm - 400cm non-contact measurement function, the ranging accuracy can reach to 3mm. The modules includes ultrasonic transmitters, receiver and control circuit.

The basic principle of work:
Using IO trigger for at least 10us high level signal,
The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back.
If the signal back, through high level , time of high output IO duration is the time from sending ultrasonic to returning. Test distance = (high level time×velocity of sound (340M/S) /2

Specifications:
Lead Free Status: Lead free / RoHS Compliant
Operating Temperature: -40°C ~ 125°C
Termination Style: Surface Mount

Working Voltage: DC 5V
Working Current: 15mA
Working Frequency: 40Hz
Max Range: 4m
Min Range: 2cm
Measuring Angle: 15 Degrees
Trigger Input Signal: 10uS TTL pulse
Echo Output Signal: Input TTL lever signal and the range in proportion
Dimension: 45 x 20 x 15mm