Add test points so we can measure voltage and current

[amcewen]

I've got some INA219 breakout boards which can monitor voltage and current.

To check the performance of the circuit (and any windmills or solar panels) it's be good to be able to monitor things at various points around the circuit:

• [x] between the rectifier circuit and the charger
• [x] between the solar connector and the charger
• [ ] between the charger and the battery

[amcewen]

As there are two sets of connections between the rectifier and the charger — so the board can be cut there and become separate "windmill rectifier" and "charger", they can be used as test points too. Similarly a solar connector to charger measurement can be done in the wiring from the solar panel.

We could do similar with the wiring for the battery, but given they've got JST plugs, it's handy to have a specific test point. I've added that: JP3. It's normally bridged, so will need to be cut if we want to test the current through it, and wires soldered to each side of the jumper.