On my FEZ Domino I have ADC pin A0 connected to a low power amplifier for the signal I want to measure. If I use the + 5v available from the FEZ board to power may amp I get a high frequency noise level of about 150 mv peak to peak (scope photo attached). If I power the amp from a separate 5 volt supply the noise level drops to less than 30 mv PP (photo attach, I would, but forum says only one).
Does anyone have any suggestions for how I might reduce the noise level when the amp is powered of the FEZ 5V pin? Tying the other A/D inputs to ground doesn’t help. It also doesn’t help if I supply the FEZ with my own 5V supply - the noise is there when the amp is powered by the FEZ.
The amp works fine with another ARM SBC I’m testing - input noise levels are less than 50 mv pp so I’m sure it’s not the amp. I’d prefer to use the FEZ so any help in reducing this noise level would be appreciated.