How Module works: 

(1) The IO trigger ranging, give the high level of the signal at least 10uSec; 
(2) Module automatically sends eight bits of 40khz square wave and automatically detect whether a signal return or not
(3) There is a signal to return, through the IO high level output, the time of high level duration is Ultrasonic time which is calculated from launch to return. 
Test distance = ( time of high level * speed of sound (340M / S)) / 2

Application Note: 

1. This module should be connected with power after connecting GND pin. Otherwise it will affect the module. 
2. The object’ area which be tested is not less than 0.5m2, and as flat as possible, otherwise it will affect the test results. 
3. If the measured test surface is irregular or distant objects, can be used to correct for multiple measurements.