Tech Support: services elecfreaks.com Ultrasonic Ranging Module HC - SR04 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 and detect 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 timevelocity of sound (340M/S) / 2, Wire connecting direct as following: 5V Supply Trigger Pulse Input Echo Pulse Output 0V Ground 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 Vcc Trig Echo GND Timing diagram The Timing diagram is shown below. You only need to supply 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 we suggest to use over 60ms measurement cycle, in order to prevent trigger signal to the echo signal.