Connecting an I2C Device to the ESP32-C3 Super Mini
Wiring
The ESP32-C3 lets you route I2C to almost any GPIO, but the Super Mini’s board silkscreen and common examples use these:
I2C device pinESP32-C3 Super Mini pin
VCC3V3 (3.3 V)
GNDGND
SDAGPIO8
SCLGPIO9
Things to watch:
GPIO8 and GPIO9 are strapping pins. GPIO9 is tied to the BOOT button, and GPIO8 is also used at boot. Many people use them for I2C successfully, but if the board won’t boot or flash, an I2C device pulling those lines low is a likely cause. Alternatives such as GPIO4 (SDA) and GPIO5 (SCL) are safer; just specify them in code.
Onboard LED: On many Super Mini boards the LED is on GPIO8 (some on GPIO10), which can cause a faint glow or slight loading on the SDA line.
Pull-ups: I2C needs pull-up resistors (typically 4.7 kΩ to 3.3 V) on SDA and SCL. Most breakout modules (OLEDs, BME280, MPU6050, etc.) already include them. If you’re using a bare chip or things are flaky, add them.
Voltage: The ESP32-C3 is 3.3 V logic and not 5 V tolerant. If your device is 5 V-only, use a level shifter.
Arduino Code
Select the board ESP32C3 Dev Module and enable USB CDC On Boot so Serial works over USB.
I2C scanner (verify your wiring)
cpp
include <Wire.h>
define SDA_PIN 8
define SCL_PIN 9
void setup() {
Serial.begin(115200);
delay(1000);
Wire.begin(SDA_PIN, SCL_PIN);
Serial.println("Scanning I2C bus...");
}
void loop() {
int found = 0;
for (uint8_t addr = 1; addr < 127; addr++) {
Wire.beginTransmission(addr);
if (Wire.endTransmission() == 0) {
Serial.print("Found device at 0x");
Serial.println(addr, HEX);
found++;
}
}
if (!found) Serial.println("No I2C devices found");
delay(3000);
}
If your device shows up (e.g. 0x3C for an SSD1306 OLED, 0x76/0x77 for a BME280, 0x68 for an MPU6050), the hardware is working.
Example: SSD1306 OLED
Install Adafruit SSD1306 and Adafruit GFX from the Library Manager:
cpp
include <Wire.h>
include <Adafruit_GFX.h>
include <Adafruit_SSD1306.h>
Adafruit_SSD1306 display(128, 64, &Wire, -1);
void setup() {
Wire.begin(8, 9);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
display.clearDisplay();
display.setTextSize(2);
display.setTextColor(SSD1306_WHITE);
display.setCursor(0, 0);
display.println("Hello C3!");
display.display();
}
void loop() {}
MicroPython
python
from machine import Pin, I2C
i2c = I2C(0, scl=Pin(9), sda=Pin(8), freq=400000)
print([hex(a) for a in i2c.scan()])
Troubleshooting
No devices found: Check that SDA and SCL aren’t swapped, GND is shared, and VCC is 3.3 V. Try a lower speed with Wire.setClock(100000);.
Can’t upload after wiring: Disconnect the I2C device (or move to GPIO4/5), then hold BOOT while plugging in USB to enter download mode.
Serial output missing: Enable USB CDC On Boot in the Tools menu.
Long wires / multiple devices: Keep wires short, use 100 kHz, and make sure addresses don’t conflict.