ADC in Atmega8 and Atmega328

[premkumar9]

Hi,
I used ADC of Atmega8 and Atmega 328. In first case I see fluctuation in the serial output value (ADC value of A0) and in the case of 328 it is more stable. I used the same program in both cases using Arduino IDE. Is this because of any difference in the ADC of these 2 ICs or some settings issue? Can anybody please help?

 

[Ian Rogers]

How much fluctuation? Is the ADC is being read more frequently on one more than the other?
The other factor is the input impedance of the two ADC modules... The later (328) is a newer chip and looking at the ADC characteristics... Seems to be a better ADC module with better non-linearity...

 

[premkumar9]

How much fluctuation? Is the ADC is being read more frequently on one more than the other?
The other factor is the input impedance of the two ADC modules... The later (328) is a newer chip and looking at the ADC characteristics... Seems to be a better ADC module with better non-linearity...

Atmega8 shows around 40mv fluctuation while 328 is about 2 mv. Reading interval is kept same. (1 sec )