Product features:
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:
(1) Using IO trigger for at least 10us high level signal,
(2) The Module automatically sends eight 40 kHz anddetect whether there is a pulse signal back.
(3) 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,

Electric Parameter
Working Voltage DC 5 V
Working Current 15mA
Working Frequency 40Hz
Max Range 4m
Min Range 2cm
MeasuringAngle 15 degree
Trigger Input Signal 10uS TTL pulse
Echo Output Signal Input TTL lever signal and the range in
proportion
Dimension 45*20*15mm

Wire connecting direct as following:
5V Supply
Trigger Pulse Input
Echo Pulse Output
0V Ground

Timing diagram
The Timing diagram is shown below. You only need tosupply a short 10uS pulse to the trigger input to start the ranging, and then the module will send out an 8 cycle burst of ultrasound at 40 kHz and raise its echo. The Echo is a distance object that is pulse width and the range in proportion .You can calculate the range through the time interval between sending trigger signal and receiving echo signal. Formula: uS / 58 = centimeters or uS / 148 =inch; or: the range = high level time * velocity (340M/S) / 2; wesuggest to use over 60ms measurement cycle, in order to prevent trigger signal to the echo signal.


Attention:
  The module is not suggested to connect directly toelectric, if connected electric, the GND terminal should be connected the module first, otherwise, it will affect the normal work of the module.
  When tested objects, the range of area is not less than 0.5 square meters and the plane requests as smooth as possible, otherwise ,it will affect the results of measuring.