The past week or so I have been exploring the use of the ATTiny841 for my programming blocks in place of the Arduino pro Mini clones I was using. There is nothing inherently wrong with the Pro Mini and they are cheap enough to use, however plopping a chip directly on the PCB will make for a more robust (and even cheaper) system. Brian Lough was experimenting with the '841 on his YouTube channel a few weeks ago and it looks to be an impressive little chip. It has 2 USARTs (which will be handy for the incoming and outgoing serial data for this project) and comes in a 14-pin package. SpenceKonde's ATTinyCore supports the chip and provides software I2C master support, although for now I am using an external library for the I2C. (I need to determine if I can change the default pins for the built-in soft I2C support - my initial attempts were not overly successful.)
I successfully breadboarded an ATTiny841-based block today and happily it seems to work fine. It looks a bit messy on the breadboard, but looks aren't everything. ;^)
Now that I have the breadboard prototype working, it is time to commit it to a PCB. Due to the relatively low GPIO pin count, I have decided to switch to a hardcoded block id, which simplifies the PCB design. I'm keeping the same form factor as the Pro Mini based design and the final product will look quite stark in comparison! Apart from the connectors, everything is now surface mount. This was not an easy decision for me, as I am through-hole through and through, but the '841 only comes in an SMT package and it just felt odd surrounding the SMT chip with a couple of THT capacitors and a handful of THT resistors and LEDs.
With luck I will be able to get these new PCBs in multiple colours so I can use the board colour to visually identify the block function. (NB: I envisage the final version of this product will be housed in coloured cases, with each case having a different shape , so the function of a block will be identified by colour and shape (and possibly texture?) so as to cater for colour-blind users. I also want to key the connectors based on block type if possible so it will be difficult (or impossible) to plug the "wrong" blocks in to each other...)