[FR] Onboard/Motherboard-based Thermistor Support

[thisiskeithb]

Description

Boards like the Einsy Rambo, BTT002, SKR E3 Turbo, and motherboard used in the Eryone ER-20 have an onboard 100K thermistor, but motherboard/onboard thermistors are not natively supported in Marlin.

There's a "hacky" way to get readings where you define the onboard thermistor as a TEMP_CHAMBER_PIN which gives you feedback on the LCD & associated thermal protections, but that's not ideal.

Feature Workflow

1. Support onboard thermistor with something like TEMP_MOTHERBOARD_PIN
2. Show temperature over serial and optionally on the LCD
3. Enjoy thermal protections of motherboard-based thermistors!

[3DFans]

thx @thisiskeithb

[ETE-Design]

Would also be great if a 2'nd bed could be added as an option... I have 2 Zone's on my bed and right now I use Chamber to show 2'nd Zone Temp... But then it also need a 2'nd Heater Pin defined to make it work...

[slowbro]

Would also be great if a 2'nd bed could be added as an option... I have 2 Zone's on my bed and right now I use Chamber to show 2'nd Zone Temp... But then it also need a 2'nd Heater Pin defined to make it work...

The "Redundant Temp Sensor" option I made would probably do this for you.

[ETE-Design]

@slowbro In this PR? Would also be great with alternative bitmap for it ;-)

[thisiskeithb]

Would also be great if a 2'nd bed could be added as an option... I have 2 Zone's on my bed and right now I use Chamber to show 2'nd Zone Temp... But then it also need a 2'nd Heater Pin defined to make it work...

This should be a different Feature Request.

[slowbro]

@slowbro In this PR? Would also be great with alternative bitmap for it ;-)

Ah, I misinterpreted your first message, I thought you were just trying to ensure the zones were the same temp. Agreed with @thisiskeithb, you should open a separate feature request for that :)

[slowbro]

Since I've been recently spending a lot of time in the temperature module, I'll take this and add a new TEMP_SENSOR_BOARD option.

[thisiskeithb]

Closing since the feature request was complete and I'll open a separate ticket if we can't figure out why it's causing lockups.

[github-actions]

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