ESP32-C3 development board with 0.42 inch OLED display and WiFi/Bluetooth (OT3345)

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. Since the pinout and display driver differ from standard ESP32 modules, please use the specific instructions below to operate the board correctly.

1. Key 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).
• Dimensions: Very compact (approx. 20x25mm).

2. Pinout & Connections (Important!)

Online documentation is often confusing. Please 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. Driving the OLED Display (Crucial)

The screen 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 <U8g2lib.h>
#include <Wire.h>

// Initialization for ESP32-C3 with I2C on pin 5 (SDA) and 6 (SCL)
// We use the standard 128x64 driver but only a portion of the screen.
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;

// Offsets are required to center the output within 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);      // Max 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 (account for xOffset and yOffset!)
  u8g2.setCursor(xOffset + 5, yOffset + 25); 
  u8g2.print("ESP32-C3");
  
  u8g2.sendBuffer(); // Send data to display
  delay(1000);
}

5. Checking Extra 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);
}