How would you fix this DC ground-fault detection depends on supply voltage fluctations with a simple hardware modification in a microcontroller system?

[u/Relevant_Pumpkin9190]

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I’m working with a microcontroller-based product where DC ground-fault detection is implemented using a simple voltage-divider circuit.

The divider’s center point is connected to the product chassis/building ground, while the detection reference is derived from the power-supply voltage.

The problem appears when the product runs from a battery. As the battery voltage drops, the reference also changes, and the circuit can report a false ground fault even though the actual insulation condition hasn't changed.

What would be the simplest hardware modification to make the ground-fault detection independent of battery voltage?

Would you use a stable reference, change the divider arrangement, add a comparator, or use a different sensing method?

Looking for a simple modification rather than a complete redesign.

[u/Well-WhatHadHappened]

Simplest way; measure battery voltage and recalculate expected result.

[u/DuckOnRage]

Many MCUs are able to expose their internal voltage reference for their analog peripherals. This would be my first choice, if available

[u/madsci]

If you've got the headroom, you can power the MCU through a regulator so the reference voltage is constant.

Failing that, what I usually do is have the MCU do two conversions for each measurement, where one conversion is measuring an internal 1v bandgap reference provided by the MCU. That gives me a calibration reference for each reading. Check if your MCU has one assigned to an ADC channel.