ESP32-C3-DevKitC-02 Pinout & GPIO Reference

(Safe pins, ADC, I²C, SPI, UART, LED)

The ESP32-C3-DevKitC-02 is Espressif’s small RISC-V dev board based on the ESP32-C3-WROOM-02 module (4 MB flash, Wi-Fi + BLE). Almost all useful GPIOs are broken out on the two headers J1 and J3.

This guide focuses on which pins you can safely use, and how to wire ADC, I²C, SPI, UART and the onboard RGB LED.

1. Board overview

Key features (DevKitC-02):

MCU: ESP32-C3 (32-bit single-core RISC-V @ up to 160 MHz)
Wireless: 2.4 GHz Wi-Fi (b/g/n) + BLE 5
Flash: 4 MB (SPI)
Power:
- via Micro-USB
- or 5 V pin
- or 3V3 pin
Onboard USB-to-UART bridge (CP2102/CH340-type, depends on revision)
BOOT button (GPIO9) + RESET button (EN/CHIP_PU)
Onboard RGB LED on GPIO8

⚠️ All I/O is 3.3 V only. Pins are not 5 V tolerant – only the 5 V pin is meant to see 5 V (goes to the regulator).

2. Pinout summary (J1 / J3 headers)

Left header (J1)

From bottom (USB side) to top (module side):

J1 Pin	Name	Description / Functions (main ones)
1	GND	Ground
2	3V3	3.3 V output (from on-board LDO)
3	3V3	3.3 V output (same rail)
4	RST	EN / CHIP_PU – reset input (active HIGH enable)
5	GND	Ground
6	GPIO4	ADC1_CH4, FSPIHD, MTMS – good GPIO/ADC
7	GPIO5	ADC2_CH0, FSPIWP, MTDI – GPIO/ADC2 (Wi-Fi caveat)
8	GPIO6	FSPICLK, MTCK – good GPIO/SPI SCLK
9	GPIO7	FSPID, MTDO – good GPIO/SPI MOSI/CS
10	GND	Ground
11	GPIO8	Onboard RGB LED data, also strapping pin
12	GPIO9	BOOT button, strapping pin
13	5V	5 V from USB (or input if powering externally)
14	5V	Same 5 V rail
15	GND	Ground

Right header (J3)

From bottom (USB side) to top:

J3 Pin	Name	Description / Functions (main ones)
1	GND	Ground
2	GPIO0	ADC1_CH0, XTAL_32K_P – GPIO/ADC, also RTC 32 kHz
3	GPIO1	ADC1_CH1, XTAL_32K_N – GPIO/ADC, also RTC 32 kHz
4	GPIO2	ADC1_CH2, FSPIQ – GPIO/ADC, strapping
5	GPIO3	ADC1_CH3 – GPIO/ADC
6	GND	Ground
7	GPIO10	FSPICS0 – good GPIO / SPI CS
8	GND	Ground

3. Safe GPIOs (quick reference)

Safest general-purpose digital pins (no special boot quirks, broken out, not tied to buttons/LED):

GPIO0, GPIO1, GPIO3, GPIO4, GPIO6, GPIO7, GPIO10

They are perfect for: buttons, relays, MOSFET gates, SPI/I²C/UART signals, etc.

Pins that are usable but need care

GPIO2, GPIO8, GPIO9 – strapping pins
- Their level at reset controls boot configuration.
- On this board:
  - GPIO8 also drives the onboard RGB LED.
  - GPIO9 is wired to the BOOT button (pulled up, button to GND).
- You can use them after boot, but avoid:
  - heavy loads
  - large capacitors
  - strong external pull-downs that might hold the pin low during reset.
GPIO5 (ADC2_CH0) – the only ADC2 pin.
- ADC2 is shared with Wi-Fi; reading it while Wi-Fi is active can fail.
- Best used for slow sensors or when Wi-Fi traffic is light.

Pins you should not use

RST / EN (CHIP_PU) – reset only, don’t use as a GPIO.
5V / 3V3 / GND – power pins only.
Internal flash pins (GPIO12–17) and USB D± pins (18,19) are not broken out on this dev board.

4. ADC pins (analog inputs)

ESP32-C3 integrates two 12-bit SAR ADCs with 6 total channels:

ADC1 (recommended):
- GPIO0, GPIO1, GPIO2, GPIO3, GPIO4
ADC2:
- GPIO5

Tips:

Use GPIO0–4 wherever possible, especially in Wi-Fi projects.
ADC is 12-bit (0–4095). Max voltage depends on attenuation (up to ~2.5 V at 11 dB).
Add a small capacitor (e.g. 100 nF) from the ADC pin to GND for more stable readings.

Example – read a potentiometer on GPIO3 (ADC1_CH3):

const int ADC_PIN = 3; // GPIO3

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);       // 0–4095
}

void loop() {
  int raw = analogRead(ADC_PIN);
  float volts = raw * 3.3 / 4095.0;  // approx, depends on attenuation
  Serial.printf("ADC raw=%d  V=%.2f\n", raw, volts);
  delay(500);
}

5. Onboard RGB LED (GPIO8)

The DevKitC-02 includes a single addressable RGB LED (WS2812-style) on GPIO8.

Powered from 3.3 V.
Use a NeoPixel / FastLED library and set data pin = 8.
Remember: GPIO8 is also a strapping pin, but the onboard circuitry is designed not to break boot.

Example – blink the onboard LED (as plain digital, not RGB):

Some Arduino cores let you treat it as a normal output:

const int LED_PIN = 8;

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

void loop() {
  digitalWrite(LED_PIN, HIGH);
  delay(500);
  digitalWrite(LED_PIN, LOW);
  delay(500);
}

For full RGB control, use Adafruit_NeoPixel or FastLED with 1 pixel on pin 8.

6. I²C pins (SDA / SCL)

The ESP32-C3’s I²C peripheral is fully remappable using the GPIO matrix – you can use almost any free GPIO.

On this board, a safe and convenient I²C pair is:

SDA = GPIO4 (J1-6)
SCL = GPIO5 or GPIO6 (J1-7 or J1-8)

Avoid using GPIO9 as SCL (strapping + BOOT button) unless you really know what you’re doing.

Example Arduino I²C setup:

#include <Wire.h>

#define SDA_PIN 4
#define SCL_PIN 6

void setup() {
  Wire.begin(SDA_PIN, SCL_PIN);
  Serial.begin(115200);
  Serial.println("I2C started on GPIO4 (SDA) / GPIO6 (SCL)");
}

7. SPI pins

ESP32-C3 has one general-purpose SPI controller (SPI2) in addition to the flash SPI. Pins can be remapped, but the FSPI-labelled pins are convenient defaults.

Recommended SPI mapping on DevKitC-02:

SCLK = GPIO6 (J1-8)
MOSI = GPIO7 (J1-9)
MISO = GPIO4 (J1-6)
CS = GPIO10 (J3-7)

This keeps all SPI signals on the left/right mid-section and avoids strapping pins.

8. UART (serial) pins

The main USB-serial connection uses the ESP32-C3’s UART0 internally (TX/RX pins aren’t broken out – they go straight to the USB-UART bridge).
For an extra UART (e.g. Serial1 in Arduino) you can map TX/RX to any free GPIO.

Typical mapping for a second UART:

TX = GPIO7
RX = GPIO6

9. Deep-sleep & wake-up notes

Any GPIO can generate interrupts while the chip is running.
For deep-sleep, ESP32-C3 uses specific RTC-capable pins (several of GPIO0–5 can be used depending on mode). Details are in the ESP32-C3 datasheet, but a practical rule:
- GPIO0–5 are the best candidates for wake-up sources.

10. “Cheat sheet” – what to use for what

Digital outputs / inputs (safe):
- GPIO0, 1, 3, 4, 6, 7, 10
ADC inputs:
- Best: GPIO0–4
- Extra (Wi-Fi-sensitive): GPIO5 (ADC2)
Onboard LED:
- GPIO8 (WS2812 RGB)
I²C (suggested):
- SDA: GPIO4
- SCL: GPIO6 (or 5)
SPI (suggested):
- SCLK: GPIO6, MOSI: GPIO7, MISO: GPIO4, CS: GPIO10
Boot-sensitive (be gentle):
- GPIO2, GPIO8, GPIO9