HC-SR04 on OLED: Live Distance Meter
Overview & Wiring
Measure distance with the HC-SR04 ultrasonic sensor and show it in big digits on the OLED - a standalone range finder.
Wiring:
OLED -> VCC=3V3, GND=GND, SDA=GPIO4, SCL=GPIO5
HC-SR04 -> VCC=5V/VIN, Trig=GPIO6, Echo=GPIO7, GND=GND
Echo outputs 5V. For a permanent build add a 1k+2k divider on Echo, or use a 3.3V-tolerant module. Fine for quick tests.
Libraries: Adafruit SSD1306, Adafruit GFX.
Circuit Diagram
Parts You Need
Source Code (Arduino / ESP32)
#include <Wire.h> // I2C for the OLED
#include <Adafruit_GFX.h> // graphics functions
#include <Adafruit_SSD1306.h> // OLED driver
Adafruit_SSD1306 display(128, 64, &Wire, -1); // 128x64 OLED over I2C
#define TRIG 6 // Trig pin fires the pulse (GPIO6)
#define ECHO 7 // Echo pin receives the reflection (GPIO7)
void setup() {
Serial.begin(115200); // Serial for debugging
Wire.begin(4, 5); // OLED I2C on GPIO4/GPIO5
display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // start OLED at 0x3C
pinMode(TRIG, OUTPUT); // Trig = output
pinMode(ECHO, INPUT); // Echo = input
}
void loop() {
// fire a clean 10us pulse to trigger the sensor
digitalWrite(TRIG, LOW); delayMicroseconds(2);
digitalWrite(TRIG, HIGH); delayMicroseconds(10);
digitalWrite(TRIG, LOW);
long dur = pulseIn(ECHO, HIGH, 30000); // round-trip time in us (30ms timeout)
float cm = dur * 0.0343 / 2; // us -> cm, halved for one-way
display.clearDisplay(); // erase previous frame
display.setTextColor(SSD1306_WHITE);
display.setTextSize(1); // small label
display.setCursor(0, 0);
display.println("Distance");
if (dur == 0) { // no echo came back
display.setTextSize(2);
display.setCursor(0, 26);
display.print("Out of range");
Serial.println("Out of range");
} else {
display.setTextSize(3); // big value font
display.setCursor(0, 22);
display.printf("%.0f", cm); // distance, no decimals
display.setTextSize(2);
display.print(" cm");
// bar: nearer = fuller (map 0..50cm across the 128px width)
int bar = map((int)cm, 0, 50, 128, 0);
if (bar < 0) bar = 0;
if (bar > 128) bar = 128;
display.fillRect(0, 56, bar, 8, SSD1306_WHITE);
Serial.printf("Distance: %.1f cm\n", cm);
}
display.display(); // push to screen
delay(150); // ~6-7 updates/sec
}