So, I’ve designed the sensor board, this is basically a break-out of an INA219 coupled with a PCA9615, for extended I²C range. If I was to use one of these on the cluster, it’s theoretically possible for me to put one up in the fuse box on the back deck, and run CAT5e down to the server rack to help measure voltage drop across that long run. Doing that with regular I²C would be insane.
Again, I’ve gone crazy with pull-up, pull-down and termination resistances, not knowing what would be needed. The schematic is nothing special.
The board wound up bigger than I’d expected, but largely because it had to accommodate fairly heavy power traces. I think I’ve got the footprint for the screw terminal blocks right. I’ve managed to cram it onto a 5cm×5cm board (two layer).
As always, you’ve got two ways of dealing with the current shunt, either hook one up externally, which means you don’t bother with the beefy power connection footprints, or you fit a surface-mount shunt on.
You’ve got full flexibility there, as well as what address to set the board to via the jumpers.
I’ll probably order some of the connectors and other parts in question, print out the board layout and test-fit everything. I’m not happy about the fact that NXP only make the PCA9615 in TSSOP, but I guess I should be thankful the part has legs.