LOLIN C3 Mini
Tiny ESP32-C3 board from Wemos with USB-C - ideal for compact, low-power IoT projects with Wi-Fi and BLE 5.
LOLIN C3 Mini Pinout
11 pins · 2.54 mm pitch
| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 0 | A0 | safe | adc | |
| 2 | 1 | A1 | safe | adc | |
| 3 | 2 | SCKA2 | strapping | adc · spi | |
| 4 | 3 | MISOA3 | safe | adc · spi | |
| 5 | 4 | MOSIA4 | strapping | adc · spi | |
| 6 | 5 | SSA5 | strapping | adc · spi | |
| 7 | 7 | LED_BUILTIN | strapping | - | |
| 8 | 8 | SDA | strapping | i2c | |
| 9 | 10 | SCL | safe | i2c | |
| 10 | 20 | RX | uart | uart | |
| 11 | 21 | TX | uart | uart |
Start with these
4 pins with no boot or system involvementFreely assignable - no strapping, flash, USB or JTAG duties. Ideal first picks for buttons, sensors and LEDs.
Fine - with a little care
7 pins · 7 things to knowSCKGPIO2 Strapping pin, but it does not select the boot mode - GPIO9 does. Espressif only recommend pulling it up against reset-time glitches. Floating by default. Strapping
A strapping pin: Espressif recommend an external pull-up against glitches at reset, so avoid heavy capacitive loads or a strong low drive here. It does not put the chip into download mode (that is GPIO9).
MOSIGPIO4 Bootstrapping pin; JTAG TMS; Flash data (FSPIHD in internal-flash models) JTAG
Used during boot; JTAG TMS for debugging; acts as Quad-SPI flash IO (hold data line) in internal-flash variants
SSGPIO5 Bootstrapping pin; JTAG TDI; Flash data (FSPIWP in internal-flash models) JTAG
Used during boot; JTAG TDI for debugging; acts as Quad-SPI flash IO (write-protect data line) in internal-flash variants
LED_BUILTINGPIO7 Bootstrapping pin; JTAG TDO; Flash data (FSPID in internal-flash models) JTAG
Used during boot; JTAG TDO for debugging; acts as Quad-SPI flash IO (data line) in internal-flash variants
SDAGPIO8 Bootstrapping pin (needs HIGH at reset); also gates ROM boot message printing (UART_PRINT_CONTROL efuse) Strapping
Must be held high during reset (if low, UART flashing/boot may not work)
RXGPIO20 UART0 RXD (default serial input) UART
Used as UART0 receive (console/bootloader); repurposing may disable serial programming and debug logs
TXGPIO21 UART0 TXD (default serial output) UART
Used as UART0 transmit (console/bootloader); repurposing may disable serial console output and printing
All 11 pins on the LOLIN C3 Mini are usable GPIO, spaced at the standard 2.54 mm pitch.
Peripheral wiring is straightforward: I²C is mapped to SDA on GPIO8 and SCL on GPIO10; the SPI bus (MOSI, MISO, SCK, SS) is broken out in full; TX/RX on GPIO21 and GPIO20 cover serial logging and flashing.
Beyond plain digital I/O you get 6 ADC-capable pins for sensors and battery monitoring.
7 of the exposed pins carry boot-time or system duties on the ESP32-C3 (SCK, MOSI, SS and 4 more) - check the guidance above before wiring anything to them. A0, A1, MISO and SCL are free of any such role - the safest first picks.
Getting started
flash your first firmware in ~2 minutesBoard: ESP32C3 Dev Module USB CDC On Boot: Enabled Flash Size: 4MB (32Mb) Flash Mode: DIO Partition Scheme: Default 4MB with spiffs (1.2MB APP/1.5MB SPIFFS) Upload Speed: 921600
// toggle GPIO0 - wire an LED and resistor to it
void setup() {
pinMode(0, OUTPUT);
}
void loop() {
digitalWrite(0, HIGH); delay(500);
digitalWrite(0, LOW); delay(500);
}[env:lolin_c3_mini]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32-c3-devkitm-1 - or type it after board =.esp32:
board: esp32-c3-devkitm-1
variant: esp32c3
framework:
type: esp-idf
# blink - GPIO0
output:
- platform: gpio
pin: 0
id: led_out
light:
- platform: binary
name: "LED"
output: led_outesp32-c3-devkitm-1 (same ids as PlatformIO).esptool.py --chip esp32c3 --port /dev/ttyACM0 \
--baud 921600 write_flash 0x0 firmware.bin--port = your /dev/tty* (macOS/Linux) or COMx (Windows).Specifications
ESP32-C3 · 34.3 × 25.4 mm · vs other ESP32 chips →Dimensions
About this board
Inside sits the ESP32-C3 - a single-core RISC-V and the budget low-power pick.
At $4.10 it's cheaper than most ESP32-C3 boards, which usually run around $10.
Around the module: an addressable RGB LED (GPIO7) and Reset/Button buttons.
It flashes over native USB - no serial-converter driver needed, which isn't a given among ESP32-C3 boards.
Where to buy
prices are typical street pricesResources
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