Ultrasonic Distance Sensor provides very short (2CM) to long-range (4M) detection and ranging. The sensor provides precise and stable non-contact distance measurements from about 2cm to 4 meters with very high accuracy. It can be easily interfaced to any microcontroller.
 
Description:
This ultrasonic sensor module can be used for measuring distance, object sensor, motion sensors etc. High sensitive module can be used with microcontroller to integrate with motion circuits to make robotic projects and other distance, position & motion sensitive products.
The module sends eight 40Khz square wave pulses and automatically detects whether it receives the returning signal. If there is a signal returning,  a high level pulse is sent on the echo pin. The length of this pulse is the time it took the signal from first triggering to the return echo.