November 10, 2020


I found one of these on Ebay and won the bid for $6.50 (and $6.00 shipping) on 11-10-2020. This board is based on the STM32F405 chip, which has 1M of flash and 192k of ram. The processor is an ARM Cortex-M4 running at

I just went to the mailbox and the package was there! I won the bid on an Olimex STM32-P405 for $6.50. Add $6 shipping and here it is for $12,50. Mouser still has them for sale at $38 each, so that is a decent deal.

Olimex makes some top quality stuff, so I am looking forward to working with this board.

Onboard is an STM32F405RGT6 chip.

The board sports an ancient USB type B connector (the square connectors you used to see on printers and external disk drives). This is quaint, but just fine by me. Let's find a cable and plug it in.

A red power LED next to the USB connector comes on. A red STAT LED blinks rapidly for a second or two. My linux machine sees absolutely nothing on the USB bus.

Another "quaint" touch is a 9 pin D connector for a serial port. It has a MAX3232 chip next to it, so it apparently supports the old serial standard of +-12 volt levels. And lucky for me, I have some USB to serial dongles with an appropriate 9 pin D on the end.


This is always the first question. What kind of bootloader does this have? How do we get code into this thing?

It has a 20 pin JTAG connector. I have a Segger J-link with a 20 pin JTAG cable. Will this work? Looking at the pinouts, it looks like trouble without a special cable.

The Nordic Semi article talks about using an ST_link adapter, so perhaps the full up JTAG will fall back to the 2 wire SWD protocol! That would be nice. The Zephyr project page mentions the same thing (without details).
Feedback? Questions? Drop me a line!

Tom's Computer Info /