Effectively switches all values related to the directionality of current
through the TEC, including current maximums. The swapped status is
stored in the flash store.
To swap current directions, use the command "pwm <ch> polarity_swapped
<bool>", where <bool> is true when TEC current direction is reversed
from the front panel markings.
This is needed for IDC cable connections, since the IDC connector and
front panel connectors have flipped polarities.
Thermostats v2.2 and below have a noisy and offset feedback current
`tec_i` caused by missing hardware on 2 MAX1968 TEC driver pins:
1. A missing RC filter on the ITEC pin that would have isolated CPU
sampling pulses from the signal; and
2. Some missing buffering on the VREF pin that would have avoided
loading the VREF signal, preventing voltage drops from the nominal 1.5V.
Since the resulting signal `tec_i` derived from these two signals can
have an error of around +/- 100mA, and readback may affect the stability
performance of the Thermostat, disable current readback entirely on
affected hardware revisions for now.
See https://github.com/sinara-hw/Thermostat/issues/117 and
https://github.com/sinara-hw/Thermostat/issues/120.
On hardware revisions v3.x and above, this would be fixed.
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>
