First of all we need to know what is meant by ultrasonic sensor ?
Ultrasonic sensor measures the distance of a target object by emitting ultrasonic sound waves, and converts the reflected sound into an electrical signal. Ultrasonic wave is defined as “inaudible sound with high frequency for human”. Ultrasonic sensors have two main components: the transmitter ( Trigger pin ) and receiver ( Echo pin ). Transmitters convert electrical signals into ultrasound, receivers convert ultrasound into electrical signals, and transceivers can both transmit and receive ultrasound. Ultrasonic sensor has four pins namely Gnd, Vcc, Trigger and Echo. Gnd is considered as the negative pin and is connected to the ground of the system. Vcc basically powers up the sensors typically 3.3 V. Trigger works as the transmitter and echo works as the receiver.
An interesting link found among my daily reading