Loading source-backed pinouts…
Microcontroller
STM32F103C8T6 "Blue Pill"
The ubiquitous low-cost STM32 board from many manufacturers, a staple for learning bare-metal Arm, STM32duino, and SWD debugging on a budget.
Processor
STM32F103C8T6 Arm Cortex-M3 @ 72 MHz
Logic
3.3 V GPIO (many pins 5 V tolerant)
Power
Micro-USB, 5 V pin, or 3.3 V pin
Format
Breadboard DIP-style board, dual pin rows
Check before wiring
- Quality varies wildly; many boards carry counterfeit or remarked chips that deviate from the datasheet.
- Early boards ship a wrong-value USB pull-up (R10) that breaks USB enumeration.
- Only FT-marked pins are 5 V tolerant; PA11/PA12 share the USB lines.
Interfaces
GPIOI2CSPIUARTADCPWMCANUSBSWDJTAG
Source-backed connector
Interactive pin map
Pin map
Connector
Blue Pill 2x20 pin headers
USB at top, component side up, 2x20 headers on both edges
Simplified technical illustration. Pin data is source-backed; verify against the linked documentation before wiring.
Hover, tap, or focus a pad to inspect a pin. Use arrow keys to move between pins.
- Silkscreen labels for the two 20-pin side headers; USB at the top, board component-side up.
- STM32F103 IO is 3.3 V; only FT-marked pins (most PA8-PA15, PB3-PB15) are 5 V tolerant. PA0-PA7, PB0/PB1 and PC13-PC15 are NOT 5 V tolerant.
- SWD debug is on PA13 (SWDIO) and PA14 (SWCLK); USB uses PA11 (D-) and PA12 (D+); onboard LED is on PC13.
All 40 pins (table)
| # | Signal | Role | Net | Also / notes |
|---|---|---|---|---|
| 1 | Power | VBAT | ||
| 2 | GPIO | LED · Onboard LED (active low); low-drive pin. | ||
| 3 | GPIO | OSC32_IN | ||
| 4 | GPIO | OSC32_OUT | ||
| 5 | ADC | WKUP / ADC0 | ||
| 6 | ADC | ADC1 | ||
| 7 | UART | UART | USART2_TX / ADC2 | |
| 8 | UART | UART | USART2_RX / ADC3 | |
| 9 | SPI | SPI | SPI1_NSS / ADC4 | |
| 10 | SPI | SPI | SPI1_SCK / ADC5 | |
| 11 | SPI | SPI | SPI1_MISO / ADC6 | |
| 12 | SPI | SPI | SPI1_MOSI / ADC7 | |
| 13 | ADC | ADC8 | ||
| 14 | ADC | ADC9 | ||
| 15 | I2C | I2C | I2C2_SCL / USART3_TX | |
| 16 | I2C | I2C | I2C2_SDA / USART3_RX | |
| 17 | System | NRST | ||
| 18 | Power | 3V3 | ||
| 19 | Ground | GND | ||
| 20 | Ground | GND | ||
| 40 | Power | 3V3 | ||
| 39 | Ground | GND | ||
| 38 | Power | 5V | ||
| 37 | I2C | I2C | I2C1_SDA / TIM4_CH4 | |
| 36 | I2C | I2C | I2C1_SCL / TIM4_CH3 | |
| 35 | I2C | I2C | I2C1_SDA / TIM4_CH2 | |
| 34 | I2C | I2C | I2C1_SCL / TIM4_CH1 | |
| 33 | SPI | SPI | SPI1_MOSI | |
| 32 | SPI | SPI | SPI1_MISO | |
| 31 | SPI | SPI | SPI1_SCK | |
| 30 | SPI | SPI | SPI1_NSS | |
| 29 | Alt | USB_D+ / CAN_TX · Shared with USB D+. | ||
| 28 | Alt | USB_D- / CAN_RX · Shared with USB D-. | ||
| 27 | UART | UART | USART1_RX | |
| 26 | UART | UART | USART1_TX | |
| 25 | GPIO | TIM1_CH1 | ||
| 24 | SPI | SPI | SPI2_MOSI | |
| 23 | SPI | SPI | SPI2_MISO | |
| 22 | SPI | SPI | SPI2_SCK | |
| 21 | SPI | SPI | SPI2_NSS |
Why it matters
- Huge community support and cheap ST-LINK programming over the 4-pin SWD header.
- Many GPIOs are 5 V tolerant (FT pins), unusual for 3.3 V boards.
- BOOT0/BOOT1 jumpers select flash, system bootloader, or SRAM boot.
Keep exploring
Similar boards
Adafruit ESP32-S3 Feather
same microcontroller platform · 7 shared interfaces
Adafruit Feather M4 Express
same microcontroller class · same microcontroller platform
Adafruit Feather nRF52840 Express
same microcontroller platform · 7 shared interfaces
Adafruit Feather RP2040
same microcontroller class · same microcontroller platform