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MemberFebruary 25, 2021 at 8:00 pm
Regarding your suggestion of using the AREF pin.
If you open the microcontroller manual https://ww1.microchip.com/downloads/en/DeviceDoc/ATmega640-1280-1281-2560-2561-Datasheet-DS40002211A.pdf, there on page 9, chapter “2.3 Pin Descriptions” you can read:
AVCC is the supply voltage pin for Port F and the A/D Converter. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.
Therefore we can assume AVCC = VCC = 4.874V as measured before.
When you scroll down to page 365, chapter ” 31.8 ADC Characteristics” you will discover that:
Vref_MIN = 1.0V and Vref_MAX = AVCC
Because we know from above that AVCC = VCC, so AREF must always be less than or equal to VCC.
If VCC = 4.874V, as demonstrated before, then supplying 5V to AREF without supplying 5V to VCC as well is out of specification.
This suggestion could be dangerous, don’t you think so?
- This reply was modified 1 month, 2 weeks ago by Friedl. Reason: typo