Phew, that was definitely the densest board I've routed. I was really close to simply running out of room and having to make it a 4 layer board and start over. 

And here it is after removing one of the D's

So I was talking to [Stephan Bourgeois] who is working on his really cool MicroMaster Mini (seriously, take a second to look at that firmware, it's ridiculously good and I'm super jealous) and he thought it would be nice to be able to plug it in to breadWare and get the much higher performance protocol analysis and injection stuff you'd get from a dedicated piece of purpose-built hardware. So I threw in another 20-pin card-edge connector that allows them to both speak UART to each other and route signals anywhere so we can eventually add support for that. 

Also, I had forgotten about the chip shortage for a while until I was buying parts for this, and it turns out the MCP2221A UART-USB bridge might be impossible to get, so I added a footprint for the FTDI FT231XS just in case. The FT231X apparently wants resistors on the data lines while the MCP2221A doesn't, so I made a resistor footprint with bridged pads so we can have the option depending on which one gets populated. So hopefully I'm now half as likely to get screwed over by chip availability. 

This thing should just come with an xacto knife for how many solder jumpers there are.

Chip availability might also be a problem for the MCP4728 and MCP4661 but I decided I'm just going to hope for the best with those instead of covering the board in unpopulated footprints. 

And it's not like I had a ton of extra room for that

But it's finished, now I just need to do the top board (which will definitely be 4-layers, so it should be a little easier if I can get my brain to intuitively switch between 4 layers without having to think about it.