To clarify, your entire Arduino script is just that one line in setup? (And nothing in Loop?). If so, then the Quarto is setting the DAC value once and then doing nothing, so it is strange that the DAC output value would change. (If this isn't what you are running, can you try running the simple script you posted and see if that makes a difference?) I don't know what would cause this behavior, but I have some questions to help figure out what's going on:
- Can you describe how you are measuring the output? What is the bandwidth of the measurement and how often are you taking a measurement?
- Is the Quarto DAC output connected to anything besides what you are using to measure the output?
- Can you measure the DAC output with a multi-meter (and nothing else connected)? I would expect the output to read very close to 0.800V
- Can you look at the DAC output on an oscilloscope? If the output is really jumping by 60mV, hopefully you can see that and learn how often it is jumping, what the shape of the transition look like, etc.
- If you set the DAC to, 0V do you see this same behavior (but centered at 0V) or does it go away? (If not, can you unplug power to the Quarto and confirm that then the signal is stable?) What about if the output is centered at 200mV instead of 800mV, do the jumps scale down to about 20mV?
