ESP32-C3 development board with mini 0.42-inch MIDI OLED display

Product manual: ESP32-C3 Development Board with 0.42" OLED

This compact IoT board is based on the ESP32-C3 (RISC-V) chip and features an integrated 0.42 inch OLED display. Because the pinout and the display control differ from standard ESP32 modules, you will find the specific instructions below to use the board correctly.

1. Important Hardware Specifications

• Chip: ESP32-C3FN4 (4MB Flash, WiFi & Bluetooth 5.0).
• USB: Native USB (USB-C). Note: enable "USB CDC On Boot" in Arduino IDE for Serial Monitor support.
• OLED Display: 0.42 inch (effective resolution 72x40 pixels).
• Size: Very compact (approx. 20x25mm).

2. Pinout & Connections (Note!)

The online documentation is often confusing. Use the pin assignments below for this specific board (ABRobot style):

• OLED I2C SDA: GPIO 5 (Not 8, as often stated in schematics).
• OLED I2C SCL: GPIO 6 (Not 9).
• Onboard LED: GPIO 8 (Active LOW: LOW = on, HIGH = off).
• Boot Button: GPIO 9.
• Hardware Serial (UART0): TX = GPIO 21, RX = GPIO 20.

3. Arduino IDE Settings

To program this board, select the following settings in the Arduino IDE:

• Board: ESP32C3 Dev Module
• USB CDC On Boot: Enabled (Essential to see Serial.print output).
• Flash Mode: DIO (default).

4. Controlling the OLED Display (Crucial)

The display uses an SSD1306 controller, but has a physical resolution of only 72x40 pixels. However, the internal buffer is 128x64. You must apply an "offset" to make text visible.

Required Library: Install the U8g2 library (by olikraus) via the Arduino Library Manager.

Example code:

#include 
#include 

// Initialization for ESP32-C3 with I2C on pin 5 (SDA) and 6 (SCL)
// We use the standard 128x64 driver, but only part of the display.
U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE, 6, 5);

// Settings for the 0.42 inch display
int width = 72;
int height = 40;

// The offsets are needed to center the output in the 128x64 buffer
int xOffset = 30; // 30 works best in practice
int yOffset = 12; // (64 - 40) / 2 = 12

void setup(void) {
  delay(1000); // Short pause for stability
  
  u8g2.begin();
  u8g2.setContrast(255);      // Maximum brightness
  u8g2.setBusClock(400000);   // 400kHz I2C speed
  u8g2.setFont(u8g2_font_ncenB10_tr); // Choose a readable font
}

void loop(void) {
  u8g2.clearBuffer(); // Clear internal buffer
  
  // Draw a frame to test the visible area
  u8g2.drawFrame(xOffset, yOffset, width, height);
  
  // Draw text (take xOffset and yOffset into account!)
  u8g2.setCursor(xOffset + 5, yOffset + 25); 
  u8g2.print("ESP32-C3");
  
  u8g2.sendBuffer(); // Send data to the display
  delay(1000);
}

5. Check Additional Pins (LED Blink)

Want to test the other pins? Use this simple loop. Note: pin 8 also controls the onboard LED.

// GPIO 8 is the Onboard LED (LOW = ON)
#define LED_PIN 8 

void setup() {
  pinMode(LED_PIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_PIN, LOW);  // LED On
  delay(500);
  digitalWrite(LED_PIN, HIGH); // LED Off
  delay(500);
}