I’m very interested in your work – it’ll potentially save me a bunch of time porting the software. Please contact me off-line at ianf () freislich ! nom ! za and I’ll share my work. If you’re located in the USA I’ll make another board and post it you. It’s not yet ready for prime-time but I’ve attached a picture of the 3rd prototype board I made yesterday (changes are the micro SD and DS3231 RTC). I need to figure out what’s wrong with the SD interface and the soldering is rubbish because I had to de-solder and then re-solder most of the components by hand. This is the first board I made in my T-962A reflow oven and there were a bunch of shorted tracks. I’ve kept the layout single sided so I can run the boards off by hand while it still under development.
Truth be told, I’m considering loosing the 74HC595 shift register in favour of the PCF8574 I2C PIO chip. It will fee up some pins and simplify things somewhat including expansion board detection which can just be done with an I2C scan and DIP switches to set the address of the expansion board.