DFRobot Gravity: URM09 Ultrasonic Sensor (Trig) is a non-contact ultrasonic ranging sensor of high-performance from URM09 series. It employs a standard PH2.0-3P Gravity vertical interface, with an accuracy of 1% within an effective measuring range of 2~500cm (test on a flat wall). Similar to SR04 ultrasonic ranging modules in principle and using method, the ranging function of this sensor is triggered by high/low-level output from the I/O ports of a host. Then the sensor converts ultrasonic flight time into a high pulse to output. The difference is that this sensor multiplexes input and output signals onto one signal port, which allows users to easily use the sensor for distance measurement only by one I/O port of a controller.