Reverse temperature fan

[dingyifei]

Replace #4983 with PID reverse temperature fan implemented as well

Waiting for testers

High-level description:

It flips the sign of temperature difference to reverse the fan on/off

[KevinOConnor]

Thanks. As high-level feedback, it's not clear to me how this is used (and thus how many people might find it useful). If this is to heat a chamber, wouldn't it be simpler to just turn the fan on during chamber heating?

-Kevin

[dewi-ny-je]

Wouldn't changing sign of pid_Kp do the same?

[jschuh]

The use case is where the bed_heater doubles as a weak chamber heater by recirculating air under it, typically by mounting radial fans with the intake facing up in front of the bed and the exhaust just underneath. It's a relatively popular Voron mod.

FWIW, I briefly had a printer set up like this, but I controlled it by configuring the fans as heater_generic with verify_heater settings that ensured it couldn't inadvertently throw a heater_fault. It's a bit hacky, but as I recall it worked fine.

[KevinOConnor]

Thanks. I think I understand. I'm not sure about this change though. I'm not sure how many users would find it in the config and utilize it.

One of the things I was looking at was extending the "display_template" system to fan_generic - and thus allowing users to set an arbitrary math formula for the fan speed. I wonder if this may be more flexible than adding config entries to temperature_fan.

-Kevin

[dingyifei]

Sounds good. I'll close this now.