What is it?

It's a small breakout board for the ARM Cortex-M0 STM32F042 chips in TSSOP-20 packages. These very cute chips are hand-solderable but still very small, have USB capability, and a built-in DFU bootloader in ROM. They come in 2 varieties, one with 16kB flash and one with 32kB flash. Both have 6kB of SRAM. The usual capabilities (timers, I2C, SPI, UART) are of course present as well. For a detailed list of capabilities, see the datasheet.

The board is made to be analogue-friendly: the analogue voltage source (VDDA) is connected to the main voltage regulator output through a ferrite bead, and there's an extra 1uF capacitor on VDDA as well.

This board itself breaks out all the MCU's pins, comes with a mini USB connector and the SWD debug pins are broken out again at the short side of the PCB for an easy debugging access. Furthermore there is one onboard (amber) LED, and apart from the RESET button there is also a button hooked to the PB8/BOOT0 pin. This button can be used as a normal button by the firmware.

This means that to program the chip simply hold the PB8/BOOT0 while pressing the RESET (or powering up the chip), and it enters the bootloader. This is a hardware feature, so it always works, even if the actual firmware doesn't cooperate.

The boards have been hand-soldered by me. The design is open:

• EAGLE sources
• schematic
• PCB on OSH Park (should you prefer to make one yourself)

Why did you make it?

I wanted to play with the STM32F042 chips and I like making small breakouts ;)