What happen when a voltage measured by analogRead() is higher than AREF voltage?

Example: AREF = 2.5V AO = 3.2V

What is the maximum voltage ?

  • 1
    About which microcontroller are you asking? Normally AREF must be within a rather small range around Vcc.
    – chrisl
    Jun 20, 2022 at 9:57
  • AREF is basically top value of ADC, AVCC must be around Vcc. If your AO will be bigger than Vcc, then internal protection diodes takes place (so Vcc might be pulled to AO level, eventually protection diode might get destroyed by over current, or MCU by overvoltage)
    – KIIV
    Jun 20, 2022 at 13:06

1 Answer 1


You will be reading the maximum ADC value. If you were sampling a waveform the top of it would be clipped off at 2.5v.

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