SSD1306 OLED display with Arduino: I²C wiring and drawing code

#What it is

This is a tiny 0.96-inch screen with 128 × 64 pixels, driven by a chip called the SSD1306. Each pixel is its own little light (that is what OLED means: organic LED), so there is no backlight — black is truly black and the text is sharp and bright.

It talks to the Arduino over I²C, a way to send data on just two wires. With power and ground that makes four pins in total. See it in 3D.

#How it works

#I²C: two wires, many devices

I²C (say "I-squared-C") uses one wire for the clock, SCL, and one for the data, SDA. Every device on the wires has an address; this screen answers to 0x3C. The Arduino says "0x3C, listen", then sends bytes. On the UNO, I²C lives on fixed pins: SDA is A4 and SCL is A5.

#The picture is in memory

The screen keeps the picture in 1 KB of memory: 128 × 64 pixels ÷ 8 = 1024 bytes. Each byte holds a column of 8 pixels stacked on top of each other, so the screen is split into 8 horizontal bands (called pages) of 128 bytes.

Your sketch never draws straight onto the glass. The library keeps a copy of that 1 KB in the Arduino's RAM, you draw into the copy, and display() sends the whole picture over I²C in one go. Our 3D lab simulates the real SSD1306 commands, byte by byte, so the 3D screen shows exactly what your code sent.

#Pins

#How to wire it to an Arduino

Four jumper wires, no breadboard:

1. GND → GND
2. VCC → 5V
3. SCL → A5
4. SDA → A4

Play in 3DRun the code · press the parts · turn it around

#Example code

From the plant monitor, which shows soil moisture as a number, a bar and a mood:

#include <OLED.h>
OLED screen;
const int SENSOR = A0;
const int DRY = 520, WET = 260;   // readings in dry air and in water

void setup() {
  screen.begin();
  Serial.begin(9600);
}

void loop() {
  int raw = analogRead(SENSOR);
  int percent = constrain(map(raw, DRY, WET, 0, 100), 0, 100);
  Serial.println(percent);

  screen.clearDisplay();
  screen.setTextSize(3);
  screen.setCursor(0, 0);
  screen.print(percent);
  screen.print("%");
  screen.drawRect(0, 28, 128, 10, WHITE);
  screen.fillRect(2, 30, percent * 124 / 100, 6, WHITE);
  screen.setTextSize(2);
  screen.setCursor(0, 46);
  if (percent < 30) screen.print("Water me!");
  else if (percent > 85) screen.print("Too wet!");
  else screen.print("Happy :)");
  screen.display();
  delay(500);
}

• #include <OLED.h> and OLED screen; — our 3D lab's small OLED library. screen.begin() sets the screen up at address 0x3C.
• clearDisplay() wipes the copy in RAM (not the glass — yet).
• setTextSize(3) makes letters 18 × 24 pixels; setCursor(0, 0) puts the next text in the top-left corner. x goes right, y goes down.
• drawRect(0, 28, 128, 10, WHITE) draws an outline: x, y, width, height. fillRect(...) fills one — here a bar percent * 124 / 100 pixels long.
• display() sends the finished picture. Forget it and the screen never changes.

#Common mistakes

• The screen stays black. No display() call, SDA and SCL swapped, or the wrong address. Most 0.96" modules use 0x3C; a few use 0x3D.
• Old text is still there. Call clearDisplay() before drawing a new frame, or the new picture is drawn over the old one.
• Text runs off the edge. At size 2 only 10 letters fit on a line; the rest wraps to the next line.
• SDA/SCL on other pins. On the UNO, I²C is only on A4 and A5 (also copied to the two pins next to AREF).

#Check yourself

#Questions people ask

#What is the I²C address of the SSD1306 OLED?

Almost always 0x3C. Some modules use 0x3D (often marked "0x7A/0x78" on the back, which are the same addresses written differently). An I²C scanner sketch will tell you for sure.

#Can I use the OLED with other I²C sensors?

Yes. I²C is a shared bus: several devices hang on the same SDA and SCL wires, each with its own address.

#Why is my OLED display upside down?

The screen can be flipped by a command; libraries offer setRotation(2) (Adafruit) to turn it 180°.

#Where it is used

The OLED is the face of the plant monitor, together with the capacitive soil moisture sensor.

Last updated 2026-10-29