STM32F103C8T6 MCU minimum system board, size 31.54mm×40mm, very small,

suitable for embedding in your own project, all 34 IO ports are led out,

the spacing is set, you can plug directly into the hole board,

input voltage 5V, SW debugging The pins are led out separately.

There are many ways to download the program,

I use the serial download method. 

Use a USB to TTL module, BOOT0 pulls down by default,

use a jumper cap to connect to VCC, PA9-RX, PA10-TX,

and then connect the module to the computer,

use the serial port to download the software to download the program.

There is a chip, pin header and an R5 missing in the BOM.

The chip and pin header are cheaper.

The resistance value of R5 can be changed.

Don’t be too small or too big.

There is no need to buy the same 620Ω.