Note: This board is deprecated in favor of SushiBits One which fixed USB and comes with a wide choice of chips.

So your project happened to outgrow Arduino Zero or Uno, but stepping up to Due or Mega seemed too much? This board can be a solution to that.

Specification

3.3V, ARM architecture, Cortex-M3 @ 72MHz (32MHz ultra low power option)

• Microcontroller options:
  • STM32F103CBT (LQFP48 package), operating at 72MHz, 128kB Flash, 20kB SRAM
  • STM32L151CCT (LQFP48 package), ultra low power, operating at 32MHz, 256kB Flash, 32kB SRAM)
  • ARM Cortex-M3 architecture
  • ARMv7-M instruction set
• Onboard 8MHz high-speed crystal for main PLL and 32768Hz watch crystal for RTC
• Two USB 2.0 Full-Speed interfaces: one native to the processor, one for on-board USB to Serial adapter
• CR1220 Backup battery for real-time clock
• Switch-mode power architecture for ultra low power operation

This board comes in the same physical dimensions as Arduino Uno and follows the Arduino 1.0 pinout, and existing shields should fit.

Story of Creation

This design is one of my post-graduation design challenges: try to design a board around STM32 MCU that:

• Arduino-compatible,
• Breaks all I/O pins on the chip out one way or another (I/O, JTAG and USB),
• 2 layers only,
• Single-side load,
• Switch-mode power architecture.

This board came out of that challenge, and worked fairly well as a general development board. Also ST doesn't have a Discovery kit for ATM32F103 series, this board may serve that purpose too.

Next revision

I have already planned the next revision, and sales on this design will go into building that. The next revision will have the following additional features:

• Onboard JTAG programmer and debugger based on CMSIS-DAP and another STM32F103 chip
• Improved USB wiring that allows for lazier boot sequence and re-enumerating