Hi,
Just a guess but one of the input protection diodes could have shorted out if the input went too high or too low for a moment. That would cause any input to be changed by the ADC itself.
Try a different channel or change the ADC unit altogether and try again.
Be sure the input can never go higher than +Vcc of the ADC or lower than 0v of the ADC.
Connect a 1k resistor in series with the ADC input if you suspect the divider is allowing a voltage too high or too low from noise or other source.
Once the diode shorts it's impossible to use that channel, and it may mess up the entire ADC chip.
Just a guess but one of the input protection diodes could have shorted out if the input went too high or too low for a moment. That would cause any input to be changed by the ADC itself.
Try a different channel or change the ADC unit altogether and try again.
Be sure the input can never go higher than +Vcc of the ADC or lower than 0v of the ADC.
Connect a 1k resistor in series with the ADC input if you suspect the divider is allowing a voltage too high or too low from noise or other source.
Once the diode shorts it's impossible to use that channel, and it may mess up the entire ADC chip.