Change the behaviour of LED L3 to turn off only when all channels have
PID disengaged, as opposed to when any channel disengages PID.
Otherwise, when disengaging PID on a Thermostat that has had both
channels engaged in PID, the LED would turn off, even when PID is still
engaged on the other channel.
This lets the LED better reflect the status of the Thermostat as a
whole, as it would stay on as long as PID is engaged on at least one
channel.
Rewrite of PID according to https://hackmd.io/IACbwcOTSt6Adj3_F9bKuw PID implementation.
To migrate:
- TEC+/- pin polarity has to be reversed.
- Some saved settings might be wiped upon flashing of new firmware, back up settings before upgrade
- Min / Max integral parameters no longer exist
- kp, ki, kd will likely need to be retuned
The software has been tested on hardware with good temperature control stability.
Reviewed-on: M-Labs/thermostat#68
Co-authored-by: topquark12 <aw@m-labs.hk>
Co-committed-by: topquark12 <aw@m-labs.hk>
