Distance meter

Why it’s here

Move the obstacle and compare echo time, the numeric display and the bar.

How it works

Time an ultrasonic echo and show centimeters on an OLED. The pulse travels to the obstacle and back. Distance uses only the one-way travel. This guided model targets the original ESP32 and Arduino-ESP32 3.x; radio, acoustics, loads and mechanics are simplified.

Try it

1. Open this experiment
2. Move the obstacle and compare echo time, the numeric display and the bar.

Connections

• GPIO 5 / 19 — TRIG / 3.3V-compatible ECHO
• GPIO 21 / 22 — OLED SDA / SCL · 3V3/GND

Example sketch

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
Adafruit_SSD1306 display(128, 64, &Wire, -1);
// Use a 3.3V-compatible HC-SR04P. A 5V ECHO needs a divider.

void setup() {
  Serial.begin(115200);
  pinMode(5, OUTPUT); pinMode(19, INPUT);
  Wire.begin(21, 22);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
}

void loop() {
  digitalWrite(5, LOW); delayMicroseconds(2);
  digitalWrite(5, HIGH); delayMicroseconds(10);
  digitalWrite(5, LOW);
  unsigned long echo = pulseIn(19, HIGH, 30000);
  float cm = echo ? echo / 58.0f : -1;
  display.clearDisplay(); display.setTextColor(SSD1306_WHITE);
  display.setTextSize(2); display.setCursor(0, 0);
  if (cm < 0) display.print("No echo"); else { display.print(cm, 1); display.print(" cm"); }
  display.display(); Serial.println(cm);
  delay(100);
}

Check your understanding

Why divide the round-trip time by two?