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OLED Distance Meter

A meter that shows the distance measured by an HC-SR04 on a 0.96" OLED screen, no computer needed: the distance in large text on top, and below it a bar graph of the last 128 readings scrolling to the right. Move your hand closer and further and watch the graph rise and fall. It teaches driving a screen over I2C, drawing text and lines with Adafruit GFX, keeping readings in a ring buffer, and timing with millis() instead of delay. Install the "Adafruit SSD1306" and "Adafruit GFX" libraries from the Library Manager.

What you need

• 1 × Arduino Uno R3
• 1 × Breadboard 830 Points (MB-102)
• 1 × HC-SR04 Ultrasonic Distance Sensor
• 1 × 0.96" OLED Display (SSD1306, I2C)
• 6 × Jumper Wire - Male/Male
• 4 × Jumper Wire - Male/Female

Wiring steps

1. 1

   Connect the power rails (5V and GND)

   

   Plug a red jumper wire into the 5V pin on the Arduino's power header and connect its other end to the breadboard's bottom red (+) rail. Plug a black wire into one of the GND pins on the same header and connect its other end to the bottom blue (−) rail. The Uno has a single 5V pin; these two rails share 5V and GND between the sensor and the screen.

   • Arduino 5V → the bottom red (+) rail (red wire)
   • Arduino GND → the bottom blue (−) rail (black wire)
2. 2

   Add and wire the HC-SR04

   

   Plug the HC-SR04 upright into the top half of the breadboard, its "eyes" facing the way it will measure; its four legs go, from left to right, VCC in column 7, TRIG in 8, ECHO in 9 and GND in 10. Connect column 7 (VCC) to the bottom (+) rail with a red wire and column 10 (GND) to the bottom (−) rail with a black wire. Connect the Arduino's pin 7 to column 8 with a blue wire (TRIG_PIN 7) and its pin 8 to column 9 with a yellow wire (ECHO_PIN 8). The pin numbers and the column numbers differ; go by the columns.

   • HC-SR04 VCC → column 7, top half
   • HC-SR04 TRIG → column 8, top half
   • HC-SR04 ECHO → column 9, top half
   • HC-SR04 GND → column 10, top half
   • column 7, top half → the bottom red (+) rail (red wire)
   • column 10, top half → the bottom blue (−) rail (black wire)
   • Arduino pin 7 → column 8, top half (blue wire)
   • Arduino pin 8 → column 9, top half (yellow wire)
3. 3

   Connect the OLED

   

   Do not plug the screen into the breadboard; push the female ends of male-female jumper wires onto its four pins. Connect VCC to the bottom (+) rail and GND to the bottom (−) rail. Connect SDA to the Arduino's A4 pin with a brown wire and SCL to A5 with a green wire. The pin order varies from screen to screen (on some VCC comes first): read the labels on the board before wiring. These screens also run on 5V; thanks to I2C all 128x64 pixels are driven over these two data wires.

   • OLED screen GND → the bottom blue (−) rail (black wire)
   • OLED screen VCC → the bottom red (+) rail (red wire)
   • Arduino A4 → OLED screen SDA (brown wire)
   • Arduino A5 → OLED screen SCL (green wire)

Arduino sketch

// Install from the Library Manager:
// "Adafruit SSD1306" and "Adafruit GFX"
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// HC-SR04 pins
const int TRIG_PIN = 7;
const int ECHO_PIN = 8;

// Graph ceiling (cm): further sits on top
const int MAX_CM = 100;
// Graph area: the screen's bottom 40 rows
const int GRAPH_TOP = 24;
const int GRAPH_H = 40;
// Time between readings (ms)
const unsigned long MEASURE_EVERY = 100;

// 128x64 screen; I2C address mostly 0x3C
Adafruit_SSD1306 oled(128, 64, &Wire, -1);

// The last 128 readings, one per column
byte history[128];
int newest = 0;
unsigned long lastMeasure = 0;

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);

  if (!oled.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED not found");
    // No screen: stop here
    while (true) {}
  }
  oled.setTextColor(SSD1306_WHITE);
}

// Distance in cm; -1 when no echo comes
int measureCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  unsigned long echo = pulseIn(ECHO_PIN, HIGH, 30000);
  if (echo == 0) {
    return -1;
  }
  return echo / 58;
}

// Distance on top, recent readings below
void draw(int cm) {
  oled.clearDisplay();
  oled.setTextSize(2);
  oled.setCursor(0, 0);
  if (cm < 0) {
    oled.print("-- cm");
  } else {
    oled.print(cm);
    oled.print(" cm");
  }

  // Oldest reading left, newest right
  for (int x = 0; x < 128; x++) {
    int h = history[(newest + 1 + x) % 128];
    int bottom = GRAPH_TOP + GRAPH_H - 1;
    oled.drawFastVLine(x, bottom - h, h + 1, SSD1306_WHITE);
  }
  oled.display();
}

void loop() {
  if (millis() - lastMeasure < MEASURE_EVERY) {
    return;
  }
  lastMeasure = millis();
  int cm = measureCm();

  // Unmeasured or too far: right on top
  int shown = (cm < 0 || cm > MAX_CM) ? MAX_CM : cm;
  newest = (newest + 1) % 128;
  history[newest] = map(shown, 0, MAX_CM, 0, GRAPH_H - 1);

  draw(cm);
  if (cm < 0) {
    Serial.println("Distance: no reading");
  } else {
    Serial.print("Distance: ");
    Serial.print(cm);
    Serial.println(" cm");
  }
}

What the Serial Monitor shows

Distance: 87 cm
Distance: 64 cm
Distance: 31 cm
Distance: 12 cm
Distance: no reading

If a wire is loose

OLED not found

What you will see

The top of the screen shows the distance in large text (for example 25 cm), and below it a bar graph moves one step to the right every tenth of a second: the taller the bar, the further away the obstacle. Bring your hand closer and the bars shrink, move it away and they grow; readings over a metre or with no echo sit on top. If the screen stays dark, check the Serial Monitor: if it says "OLED not found", check that SDA is on A4, SCL on A5, and VCC/GND; your screen's address may be 0x3D, so change 0x3C in the code to 0x3D. If the distance always reads "--", check the TRIG and ECHO wires.