Oct 212018
 

So, I placed an order to Mouser the other day to actually get some parts into my hands so I can better design the boards.

In that, I discovered the screw terminals I was planning on using, are discontinued.  So, I found something that was able to take the same gauge wire: Phoenix 1017526s.  Turns out, these will not fit along side the current shunts on the board as planned.

There’s just no way I’ll be fitting these on a 5×5cm board and have room to spare for a shunt in between.  Since this is really application-specific, it might be better off board.  We’ll put the INA219 and PCA9615 together on the board so we have a nice self-contained sensor board that can be mounted close to the current shunt, wherever that lives, and have nice noise-resistant links back to the controller.

This does mean I can do things like put a current shunt in the fuse box where the solar panels connect, and run CAT5 down to the controller from there.

To make routing easier, I’ve gone to a 4-layer board.  The board has solder-jumpers for setting the I²C address of the INA219, and I’ve documented all the termination and pull resistors.  I’m not sure what ones are needed yet, so there’s space at every point where I could envisage one being needed.

There’s two power planes in the inner layers, one for VCC the other for 0V.

Next step, I’ll print out the board designs and test fit everything before ordering the boards, which I hope to have ordered this afternoon.

Oct 062018
 

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.