I'm currently prototyping the build, I've done a few revisions so far of the boards used in the build, I think I've settled on the backplane and control boards, but I'm waiting on the arrival of the Greenskeeper boards.

I'm hoping that they will work as intended, most of the components are through-hole, except the USB board, which uses SMD components at 0.5mm pitch that I'm not that great with soldering by hand.

I'm also working through the software side of things, and I have a pretty stable platform so far.

I was hoping to utilise i2c interrupts on the Greenskeeper board to trigger events, but I need to spend some more time looking into that, currently there is a function that runs every second to poll the Greenskeeper bus and checks for status changes.

There is the ability to start/stop/hardstop individual caddies, there are jumpers on each control board that are used to determine the type of device that is inserted, currently 8 device types are configurable.

Control boards also have USB pass through to the backplane, so you can insert a USB->SERTTL adaptor for connecting to the serial console on the Raspberry Pi inside the caddy, there are udev rules that need to be configured for this to work though, but with the use of the Greenskeeper USB board, these will be easier to set up.

The control board contains an attiny85 with some code that is used to power on/power off devices that are connected to the screw terminals, for switching 5v only. 12v is listed on the card slot that could be used to pass through 12v from the backplane, but this is unused currently, as everything I've planned around this is 5v based. There are 3 jumpers that are used to set the caddy type, using binary 1,2,4 to get combinations from 0-7 to indicate the type, this is read in by the Greenskeeper board.

The caddies are fully 3d printable, but I have laser cut parts in acrylic to reduce print times, and only printed the parts that are not just flat panels.