For my students I have designed open source easy to use compatible  with Arduino UNO board with STM32F103C8T6 chip – STM32-UNO.

Analog inputs on STM32- UNO are +5V tolerant due to passive voltage divider.

Additional UART port.

External ST Link v.2 programmer/debugger easy connected to right mounted connector. One programmer can be used for many boards.

One user red LED .

One user pushbutton.

Micro-USB port.

VBAT connector to STM32 internal  RTC.

BOOT jumpers.

Integrated with DC-DC Step-down power chips  1117XX(+5V and +3V3), it can provide highly efficient and stable power for the shields and other modules, especially suitable for those who want to build a product.

Compatibility with many Arduino UNO shields and new specially designed shields: ARMDuino –LCD1602-I2C,  ARMDuino-Multifunctional, ARMDuino-Motor Shield, ARMDuino-Impedance Meter (AD9833) also will be available on PCBWAY.COM.

I use STM32-UNO  with Keil uVision v5 IDE, and  there are many films on Yotube.com with C-coding lesson.

Why did you make it?

STM32-UNO  (now ARMDuino) is open source for everyone who ever played or want to try Arduino，Keil IDE, ST Cortex  chipset , for smart device and practical manufacturable product development . It is for students, makers , electronic Enthusiast, engineers  and designers.

Forum & documentation on

http://www.stm32duino.com/viewtopic.php?f=30&t=3218&sid=5c89e6bcabfdd93209f42bf949b0e6b1