FreePDK Padauk Programmer - Part One
A journey of 1000 miles begins with one step. Around a year ago I became aware that Dave Jones of EEVBlog fame was singing the praises of a technically capable but obscure microcontroller available for around 3 cents each in bulk.
Who wouldn't want a capable microcontroller for just a few cents? The downsides of procuring this chip for use by your average home hobbyist include:
- Non-English datasheets (slowly starting to change)
- No way to program them (unless you want to buy an expensive - almost bespoke - programmer)
- "Interesting" IDE
- Non-standard language
- Little or no online support
But that didn't stop the EEVBlog community from reverse engineering the programmer and making a PCB that is capable of transferring the required binary sequences and getting a result from these chips. The work has been amazing and about 6 months ago I decided to have a go at making one of these open source wonders.
After the usual 2020 difficulties with freight and supply I found myself in the garage at the bench with the requisite bits and pieces and a hot soldering iron. Thank you to PCBWay who manufactured and sent the PCBs all the way to Tasmania to be melted by my incompetence.
Several swearing hours later I had a mostly fused PCB that at best might be useful for shoehorning a recalcitrant foot into a tiny boot - but way short of the digital magic required to unlock an inscrutable chip!
If MKI was a mess, then MKII was even worse! Fried components, mountains of congealed flux, ripped tracks and general mayhem ensued BUT I was able to connect and program the firmware onto the STM32F072C8T6 chip. This small success was great timing because at that stage I was ready to abandon the project and admit defeat.
I've never solved a problem by giving up, and now with a sniff of success I spent a careful week, an hour here and there, putting together MKIII - which....did not work at all!
The dreaded USB connector seemed OK (after a few tries), but who knows in among that mess if any connections are actually in place - certainly the voltage checks I did seem to point to an entirely different circuit!
So with a heavy heart I reluctantly started the MKIV version. Was this going to be another waste of time? Careful soldering, careful checking and many hours later I plugged it in - and...nothing!
In the depths of despair I had a sudden flash of inspiration (or desperation) and desoldered the STM32 from the failed (but talkative) MKII board and swapped it in on the MKIV board. Hilariously I blew several components together with the hot air gun (and melted some plastic) which took a bit of sorting out.
But...success! I now have a working opensource free-pdk.github.io PCB that can load the firmware, recognise a Padauk chip AND program it to blink like a champion. What a journey. In the next blog I'll look at the programming side of this circus, er...circuit.
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