Grumpy_Mike:
Thanks for posting that.
Is there anything stoping the arduino's input from seeing a negitave voltage? That will damage it and might cause the oscillation you are seeing. Does this diasapeare when you disconnect that output from the arduino's input?
The sensor starts at .2V and goes up to 5v (though with the noise that is being generated for unknown reasons, it does seem to dip a little into the negative (no more than around .1V) since the noise has a peak-peak amplitude that is around .6V and the sensor starts at .2V ... we can't really disconnect it because it's already traced on a PCB (i.e. we're using the microcontroller loaded with the bootloader on a PCB layout) though, we did try checking an open analog input that I temporarily programmed the microcontroller to read from constantly and there was no noise being produced there. Tomorrow though we're going to try to connect the clean signal (the green box) into another Arduino we have laying around to see if when we do, it adds the same noise, but until then we're still unsure what's causing the noise, all we know is that only at points where the signal is being sent to an arduino analog input, this same noise is added (same amplitude and frequency in every case).
on a side note, we just burnt the bootloader on the atmel microcontroller (ATmega2560-16au), we didn't set any of the fuses to use an external oscillating crystal (yet, one is wired in though), could this possibly be an issue?