Microcontroller Boards

Many vendors sell a PCB containing the STM32F10C8T6 ARM microcontroller. Ebay prices including shipping are typically $2 each or even a bit less. For comparison the chip alone is well over $3 in quantity 10 from US distributors, including the trade war tariff.

This is an embedded ARM chip, targeted at the same markets as the ATmega328 in an Arduino UNO or similar board.

Advantages over an UNO copy include

• The chip has a built-in USB interface, so it doesn't need a USB-UART chip.
• With built-in USB it can be programmed to be another USB device (keyboard, mouse, audio, etc), rather than just a serial device.
• It's much faster - 72MHz.
• More peripherals - 3 UART's instead of 1, 12-bit ADC instead of 10, 2 I2C, SPI, ...

And of course some disadvantages

• Totally different pinout from any Arduino board.
• Use with Arduino IDE requires some hacking.
• Runs on 3.3 volts max. Uno can do 5.
• You will need an external USB to serial adaper to program it.

Programming Options

One option is the STM32CubeMX GUI from ST This free tool from ST has a GUI to select the peripherals in use, set clock rates, etc. It then generates skeleton code to configure everything and provides subroutines for I/O.

Another option is the libopencm3 Library. This is an old-school programming environment: it's a library to call from your own program, written with your own editor.

The stm32duino project has done a lot of work to integrate the stm32 family of chips into the Arduino framework.

Use with Arduino IDE

If you search online, people typically call this board the “Blue Pill”, from the movie, so searching online for bluepill and arduino finds lots of related information.

www.onetransistor.eu/2017/11/stm32-bluepill-arduino-ide.html has good notes on the board and how to use it with the Arduino IDE.

There is also information at wiki.stm32duino.com/index.php, but personally I found the onetransistor.eu page to be more useful.

To use it with the Arduino GUI, you need to

• Install the USB arduino interface in flash. You will need a USB to serial converter connected to the serial port of the Blue Pill for this step only. You can't use the onboard USB for initial setup, because the chip's internal bootloader doesn't support the internal USB port.
• Install the board package.