HC-SR05 ultrasonic sensor details

 (1) a IO trigger ranging is used to give at least a high signal of 10us;

(2) the module automatically sends 8 40KHz Fang Bo to automatically detect whether a signal is returned

(3) a signal is returned, and a high level of the high level is passed through the IO output. The time of the ultrasonic wave from the launch to the return. The test distance = (the high level time * sound velocity (340M/S)) /2.