• We have to figure out the distance because the sensor itself simply holds it's "ECHO" pin HIGH for a duration of time corresponding to the time it took to receive the reflection (echo) from a wave it sent.

• The module sends out a burst of sound waves, at the same time it applies voltage to the echo pin.

• The module receives the reflection back from the sound waves and removes voltage from the echo pin.

• D = 1/2 × T × C

Ultrasonic Sensor Connections

• The sensor Vcc is connected to the NodeMCU +3.3v

• The sensor GND is connected to the NodeMCU GND

• The sensor Trigger Pin is connected to the NodeMCU Digital I/O D4

• The sensor Echo Pin is connected to the NodeMCU Digital I/O D3