Ultrasonic Distance Sensor 
The Ultrasonic Distance Sensor measures distance using sound waves.
A sound is sent from one of the sensor elements and the echo is detected by the other. The time between sending and receiving signals allows the distance travelled by the echo to be calculated.
Blockly includes a special control block for this device which reports distance in cm.
Power is connected to +v and -v, whilst data using the Trigger and Echo connections.