HC-Sr504 Ultrasonic Sensor
VCC is the power supply for the HC-SR04 Ultrasonic distance sensor which we connect the 5V pin on the Arduino.
Trig (Trigger) pin is used to trigger the ultrasonic sound pulses.
Echo pin produces a pulse when the reflected signal is received. The length of the pulse is proportional to the time it took for the transmitted signal to be detected.
GND should be connected to the ground of Arduino.