# Ultrasonic Distance Meter

Day 30 of the 100 Days 100 IoT Projects collection. Board: ESP32.

An HC-SR04 measures distance in centimeters on the ESP32. Echo timing and the physics of every parking sensor.

## How it works

The board fires a trigger pulse and the HC-SR04 emits an ultrasonic burst, then listens for the echo. Distance falls out of the round-trip time: half the travel time multiplied by the speed of sound. Every parking sensor and robot bumper works on this exact principle.

## What you'll learn

- Ultrasonic time-of-flight
- Echo pulse timing
- Speed-of-sound math
- Non-contact ranging

Full project (code, wiring diagram, Wokwi simulation): https://github.com/kritishmohapatra/100_Days_100_IoT_Projects/tree/main/Ultrasonic_LED_Distance_Indicator_ESP32_MicroPython

Summary by SkillShop. Code and diagrams belong to the original repo.