Read this thread which addresses a similar problem. Note how placing a cap across the ADC input figures into things and I assume you have a cap from the power pin to ground. That may help.
thanks... i read thru that... but i already have a cap connected between aref n gnd and avcc n aref are interconnected... i still have wide fluctuations.........
Do you have a scope at your disposal to look at the actual signal input to the uC? You seem to have a handle on using caps. Noise or something is getting in there. This is where sniffing around with a scope would be nice. Including your supply power.
How much is it fluctuating? A 10-bit ADC doesn't require much 'noise' to cause what appears to be large differences. Many first time users of ADCs don't realize how sensitive they are.
Hi anita,
Try placing a resistor between the signal input and the ADC input and also maybe a small capacitor from the input to ground. May be fine after that.