lowest value on readADC?

[twisted wire]

Hi all, it's the idiot child again.....
If i reduce the supply voltage to 3vlts ( therefore the reference voltage?) what's the lowest voltage I can measure on ADC, please?
I'm using an OM2 chip and would like to measure down to millivolts if that's possible.
thanks in anticipation

 

[Engle]

Hi, OM2 chip?? With a 3.00V supply a readadc10 on my 20M2 read a 1 when the input reached about 300uV and a 1023 when it reached 2.990V. Hope that helps.