STM32 "Blue Pill"

The STM32 "Blue Pill" is a low-cost development board featuring the STM32F103C8T6, a 32-bit ARM Cortex-M3 microcontroller. It offers 64KB flash memory, 20KB SRAM, and runs at 72MHz. With multiple I/O pins, it supports UART, SPI, I2C, and USB interfaces. Ideal for hobbyists and prototyping, it’s compatible with Arduino and STM32Cube IDE, though it requires careful handling due to its basic design and limited documentation. The board also includes a real-time clock (RTC) clocked at 32MHz by a separate crystal. The microcontroller normally operates at a logic level of 3.3V. While 5V is also possible, only some of the pins are 5V-tolerant.

Features/Specifications

📄 STM32F1xxx datasheet (13119 kB)

Further Advantages over Arduino Uno/Nano

• 15 interrupt pins (Arduino has 2)
• internal pull-up AND pull-down resistors
• PWM with 16 instead of just 8 bits (65,536 instead of 255 steps)
• 12-bit instead of 10-bit ADC (analog inputs measure with 4,096 instead of 1,024 steps)
• the data type DOUBLE has 64-bit precision, unlike Arduino which only has 32-bit
• the data type LONG LONG is 64 bits long, unlike Arduino which only has 32-bit

However, the STM32 does not have a serial UART interface for programming, so you need to use a serial adapter (FTDI adapter).

Connections

Used Components

Setup for Programming

Be aware that pin layouts may vary depending on the FTDI board!

To be able to program the STM32, it must be put into programming mode. This is done by moving the upper yellow jumper (BOOT0) from position 0 to 1. Then the RESET button must be pressed. The lower jumper BOOT1 remains unchanged.

Integration into the Arduino IDE

Thanks to the STM32duino community, it is possible to fully integrate the STM32 into the Arduino IDE:

Add Board Manager

Go to the menu item Tools > Board > Boards Manager, search for Arduino SAM Boards (ARM Cortex-M3), and install this board manager:

Install STM32duino Core

Go to https://github.com/rogerclarkmelbourne/Arduino_STM32 and download the entire package as a ZIP archive (approx. 43MB). Then extract the archive and move the resulting folder Arduino_STM32 into the Arduino IDE’s sketchbook directory. (On Windows: C:\Users\YOUR_USERNAME\Documents\Arduino\hardware). If the subfolder hardware does not exist, it must be created manually. Now restart the Arduino IDE.
Under the menu item Tools > Board, the correct board can now be selected along with the appropriate options:

• Variant: STM32F103C8 (20k RAM, 64k Flash)
• CPU Speed: 72MHz (normal)
• Upload Method: Serial
• Port: [select the detected port here, e.g., COM7]

Program to test the STM32

void setup() {
    pinMode(PC13, OUTPUT); // internal LED
}

void loop() {
    digitalWrite(PC13, !digitalRead(PC13));
    delay(1000);
}

Error with Pull-Up Resistor

Unfortunately, many STM32 boards have a built-in error involving a pull-up resistor. A detailed problem description and possible solutions can be found at amitesh-singh.github.io.

Further information

• STM32-base project
• STM32 development boards