How to stabilize adc output display on 7 segment
One possible software solution is the very simple to implement exponential moving average (http://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average). It only requires one global variable and a few lines of code. It is a little more work to accomplish but this can also be done with fixed point code (ie. int) for much greater efficiency (I wouldn't worry about it if all your doing is reading an ADC and displaying it).

For example:

//K is the filter coefficient and must be smaller than 1 and greater than zero (0&lt;K&lt;1)
//The smaller the K is, the more the filter will smooth, but it will also take longer
//to reach its value when the input changes.
#define K 0.01f

float filter( float aData )
{
    static float memory;
    memory = memory*(1-K) + aData*K;
    return memory;
}