Automation pHat Reading Multiple ADC Channels


So I’m trying to use the Automation pHat ADC to sense voltage from a battery and solar panel, while also powering the raspberrypi from the battery.

The battery is being charged by the solar panel, the pi is running from battery power, through a Wide Input Shim, stacked on-top of the automation pHat. I have ADC channels connected to battery + and solar cell +.

The trouble I’m having is I can only read the voltage of the battery - I cant get the separate voltage direct from the solar cell using a separate ADC channel. I’m guessing this is because I’m using a shared ground? Because when I test the solar voltage with a multimeter it reads correctly (different to the battery)

Any ideas on whether / how I can achieve reading both voltages separately?

Thanks all!



If you simply have a solar cell connected to the battery connected to the Pi (all in parallel) then the solar cell and battery must be at the same voltage.
If you measure the solar cell when disconnected that will be quite different.
If you connect the solar cell to the battery using a schottky power diode the solar cell will be 0.2v higher than battery when sunny or a lot less when cloudy.
Or is there some sort of solar charger module in the mix there?



Yeah should have mentioned there’s a small PWM module the middle of it all - link below. I’d basically like to log both solar voltage (for interest) and battery voltage to shut the Pi down when necessary.



Put the - lead of your multimeter on the PI’s ground terminal, and the + on the solar cell + and see if you can read anything. If you can’t its likely the solar cell is isolated from the rest of the circuit by the controller. Its not sharing a common ground with the rest of the circuit.