Boards have arrived!!

A project log for Isolated ST-Link v2 with power output

A custom isolated ST-Link v2, with optional isolated 5v or 3v3 output to power circuit whilst programming/debugging.

Dr. KazDr. Kaz 08/19/2017 at 20:430 Comments

The boards and components all arrived, so today I sat to solder everything and test the module. Whilst soldering the components on, I realized I had gotten the pattern wrong for the 

After soldering all the components on, I used the ST-Link part of a STM32 discovery board I own to flash an old version of the ST-Link V2 firmware onto the board using the 

However, after the microcontroller was flashed, only the red LED was blinking at around 0.5Hz, and the unit was not connecting to the PC.

After around 4 hours of debugging, it turns out I had forgotten two things:

1. I had left the VBAT pin floating - the datasheet says that if no external battery is used, it is recommended to connect this to VCC.

2. I hadn't provided a pull-up on the USB D+ line. 

Trawling through the components I had at home, I found some 3K6 resistors, and soldered one as a pull up for the D+ pin, and hey presto, the unit was recognised as an ST-Link device on the PC.

Then I went back to the ST-Link utility and tried to update the unit to the latest ST-Link v2 software, and it worked!!

Leaving the VBAT pin unconnected wasn't such a major issue for me, and the unit worked without connecting it to VCC.

I'll modify the documents with these changes, and provide a step by step, really chuffed that it all worked.