Zitrades Module HC-SR04 Ultrasonic Distance Sensor For Arduino BY ZITRADES
PRODUCT DESCRIPTION:1.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) /22.Sensor angle: 15 to 35 degrees. Detection distance: 2cm-500cm.3.The all process is : pull the Trig pin to high level for more than 10us impulse , the module start ranging ; finish ranging , If you find an object in front , Echo pin will be high level ,  and based on the different distance,it will take the different duration of high level.4.Comes tested and sealed in ZITRADES retail ready package.