Python code to generate the LED + circular dial graphic on the web site is here: lm_wxgraphic

The ATtiny85-20 SPI authentication key chip sits in the recess of the Davis console:


I programmed and tested it on a piece of breadboard with the RPi itself using a GPIO version of avrdude:


To test, I used the bcm2835 library to access the RPi SPI:Screenshot of pi's X desktop

I had one major debug issue – quickly resolved when I noticed that the slow bit banging of SPI by the RPi worked, but the chip in situ didn’t. That was because I hadn’t programmed the CLKDIV8 fuse with avrdude and my code was running at 1MHz instead of 8MHz. I found this with the excellent Saleae Logic analyser – I also found and reported a tool bug to Saleae.

At some point I used the glorious Bus Pirate too – both for SPI testing and 3v3 RS232 level conversion now I come to think of it.