I've put together Application note 355: Digital Voice Recorder and I've run into a major problem and hope someone may have an idea what the problem may be...
While recording, I seem to be picking up a noise spike that coincidently has the same frequency as the chip select line to the DataFlash. Right now I am assuming that I am picking up some type of switching noise from the chip select line but not quite sure.
I followed the application note precisely and used standard PCB layout guidelines so I am somewhat at a loss. The one glaring difference between my design and the Appnote is that I am using the Mega128.
Now could I be picking up this noise due to:
A) Improper Grounding
B) Malfunctioning ADC channel
C) Power supply issue
D) Code problem: May be accessing the DataFlash while an ADC conversions is in progress??
Any insight to what the problem may be would be great!!