Hi Guys,
I have my little air quality control node in mind based on a Power Shield + Moteino, and with the lates addition of a Weather Shield.
As both Power Shield and Weather Shield allow Battery measurement on A7, is it better to use the Weather Shield and set A3 to trigger the MOSFET ?
For the best power savings yes. You should disable the one on the Power Shield by either not soldering that pin to the Moteino or by cutting the trace on the PShield.
So do you mean I can just unsolder/isolate A7 on the Power shield ? As the track is on the top (connector side) I can even access it :(
You can do it in many different ways. You probably want to read the WeatherShield A7 and not the PowerShield, and certainly not both!
The WS A7 will be less noisy (10K and 4.7K vs 1Meg and 470K) and will save you power when you disable the reading through A3.
Ok, so it's time for some unsoldering pump time ! :-[
I'm looking at doing the same thing, however after looking at the Power Shield i think it's more than just not connecting A7 to the header. VBAT is only on the Power Shield and that's the signal we want to measure via the Weather Shield. The Weather Shield, as far as I can tell, is setup to measure power on the VIN pin. So I'd think I should also break the connection to the VIN on the Weather Shield from the Moteino and Power Shield, and run a wire from the Power Shield's VBAT to the Weather Shield's VIN... thoughts?
Ben,
I think you got it right.
The PowerShield measures the voltage of the battery that is attached to it. The VIN on the PowerShield is actually the boosted 5V going to the Moteino.
And the WeatherShield measures the voltage on the VIN pin, which incidentally would be 5V from the PowerShield if they are stacked.
So to measure the PowerShield battery voltage with the WeatherShield you would need to:
- do not connect WShield's VIN to PShield or Moteino, instead:
- connect WShield's VIN with the PShield's battery + trace
- do not connect PShield's A7 to anything, only WShield's A7 to Moteino's A7
- disable the battery monitor on the PowerShield to give you the extra saving you're looking for otherwise you'd be better off just using the PShield's battery monitor
Double check that my logic makes sense before you solder :)