SSD1306 OLED with Seeed XIAO ESP32C3 — I2C on D4/D5

A small OLED makes a XIAO project self-contained: show a sensor value, an IP address or battery state without a laptop.

On the XIAO ESP32C3 the default I2C pins are D4 (SDA) and D5 (SCL), both free of boot duties, so the wiring is four wires and Wire.begin() with no arguments.

Wiring

Every connection
XIAO ESP32C3	SSD1306 OLED 0.96″ (128×64, I2C)	Wire
GND	GND	black
3V3	VCC	red
D5	SCL	yellow
D4	SDA	blue

3.3–5 V (on-board regulator) part, 3.3 V board. Most modules have a regulator and run from 3.3 V or 5 V. Their I2C pull-ups go to VCC, so on ESP32 and Pico power the OLED from 3.3 V to keep SDA/SCL at a safe level.

Board quirks

Unlike a generic C3 board (default I2C on the strapping pins GPIO8/9), the XIAO variant puts I2C on D4/D5 = GPIO6/7, so plain Wire.begin() is safe here.
Check the pin order printed on your OLED: some start with VCC, some with GND. Swapping them can kill the display.
Seeed’s XIAO expansion board has the same 0.96″ OLED wired to D4/D5 — this sketch runs on it unchanged.

Code

ssd1306-xiaoc3.inoArduino C++Open in Playground Flash

// SSD1306 128x64 I2C OLED on a Seeed XIAO ESP32C3.
// GND → GND, VCC → 3V3, SDA → D4 (GPIO6), SCL → D5 (GPIO7) — the XIAO's default I2C pins.
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Adafruit_SSD1306 display(128, 64, &Wire, -1);

void setup() {
  Serial.begin(115200);
  delay(1500);
  Wire.begin();  // SDA = D4, SCL = D5 on the XIAO variant
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("SSD1306 not found at 0x3C - try 0x3D, and check the GND/VCC order on your module");
    while (true) delay(1000);
  }
  display.setTextColor(SSD1306_WHITE);
  Serial.println("OLED ready");
}

void loop() {
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(0, 0);
  display.print("XIAO C3");
  display.setTextSize(1);
  display.setCursor(0, 28);
  display.printf("Uptime: %lu s", millis() / 1000);
  display.setCursor(0, 44);
  display.printf("Free heap: %u KB", ESP.getFreeHeap() / 1024);
  display.display();
  delay(1000);
}

// SSD1306 128x64 I2C OLED on a Seeed XIAO ESP32C3.
// GND → GND, VCC → 3V3, SDA → D4 (GPIO6), SCL → D5 (GPIO7) — the XIAO's default I2C pins.
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Adafruit_SSD1306 display(128, 64, &Wire, -1);

void setup() {
  Serial.begin(115200);
  delay(1500);
  Wire.begin();  // SDA = D4, SCL = D5 on the XIAO variant
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("SSD1306 not found at 0x3C - try 0x3D, and check the GND/VCC order on your module");
    while (true) delay(1000);
  }
  display.setTextColor(SSD1306_WHITE);
  Serial.println("OLED ready");
}

void loop() {
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(0, 0);
  display.print("XIAO C3");
  display.setTextSize(1);
  display.setCursor(0, 28);
  display.printf("Uptime: %lu s", millis() / 1000);
  display.setCursor(0, 44);
  display.printf("Free heap: %u KB", ESP.getFreeHeap() / 1024);
  display.display();
  delay(1000);
}

Library: Adafruit SSD1306 (Adafruit (also install Adafruit GFX Library)) — compiled with Adafruit SSD1306 2.5.17.

Expected serial output

Serial Monitor · 115200Output

OLED ready

OLED ready

Common errors

“SSD1306 not found at 0x3C”

Try 0x3D, then check SDA/SCL. Full fix.

Garbage on the right edge

It is a 1.3″ SH1106 display, not an SSD1306. Use the SH1106 library.