🩹 Add unmeasured ADC reference warning for MKS_TINYBEE board (#27434)

[fermino]

Description

MKS_TINYBEE uses a voltage reference based on a resistor-zener circuit. In some boards the zener is of dubious quality and it leads to a poor voltage reference, which in turn throws the voltage readings off (in my case, 30°C). This PR lets the user know of that with a compiler warning, so that it can be dealt with accordingly.

This follows up on #24142 and #24432, and closes #27434.

The reference circuit, out of the manufacturer's schematic:

Requirements

MKS_TINYBEE with a different voltage reference.

Benefits

It lets the user know of a common case, which can be slightly hard to track down. It allows for the related constant to be defined easily.

Configurations

Default MKS_TINYBEE.

Related Issues

#24142
#27434

[thisiskeithb]

I think this is a good idea, but you get a wall of warnings due to the many (re)includes of board pin files: https://github.com/MarlinFirmware/Marlin/actions/runs/14003259323/job/39213443240?pr=27755#step:8:49

There are a couple options:

• Add this warning via warnings.cpp if this motherobard is enabled
• Implement something like what was done for the CONTROLLER_WARNING macro if you want to halt compilation and force the user to measure their board / set the voltage / disable the warning:

  Marlin/Marlin/src/pins/pins.h

  Lines 126 to 130 in 14fa705

  	#ifndef NO_CONTROLLER_CUSTOM_WIRING_WARNING
  	#define CONTROLLER_WARNING(PF,CN,V...) static_assert(false, "\n\nWARNING! " CN " requires wiring modification! See pins_" PF ".h for details." V "\n (Define NO_CONTROLLER_CUSTOM_WIRING_WARNING to suppress this warning.)\n\n");
  	#else
  	#define CONTROLLER_WARNING(...)
  	#endif

It kind of depends on just how dodgy that part is.

[fermino]

Thanks for the feedback!

I don't have any other sample besides my own experience and the linked issues, so maybe it's not that common? I don't really know... Could it pose a security hazard? If no temperature safeguards are enabled it could be...? I might be splitting hairs here...

I think having one warning would be enough to make users aware of the problem. In the end, having a 30C difference is quite noticeable 😆

[fermino]

I just move the warning, but I don't know what the proper/expected way to do it in this codebase because something that defines ADC_REFERENCE_VOLTAGE that is being included in Warnings.cpp so the warning is not triggered properly.

[thisiskeithb]

ADC_REFERENCE_VOLTAGE is defined in the pins file / via an #ifndef, so you can simplify the #if check in the warning:#if MB(MKS_TINYBEE)

I'd change the warning too.

Combined changes look something like:

/**
 * MKS_TINYBEE Analog Reference
 */
#if MB(MKS_TINYBEE)
  #warning "If you experience odd temperature readings make sure to measure the analog reference voltage and add '#define ADC_REFERENCE_VOLTAGE <value>' to your config. See pins_MKS_TINYBEE.h for details."
#endif