My Tsunami board was delivered few days ago, it’s a great board thanks!
Could you help me with generating dc signals please, and my other question is how accurate can DC signals be? Do I need to calibrate my Tsunami and how?
As a highly unofficial answer - I guess that depends on what you would call "accurate". Don't expect anything on a millivolt (or even ten millivolts) scale - we're talking about 8 bit output DACs and 10 bit input ADCs here, and the Tsunami isn't exactly a perfectly calibrated high-precision instrument (actually the frequency precision is great, but voltages aren't particularly highly accurate). As noted in the tutorials one can actually generate DC output on the AUX output by enabling a filtered arbitrary duty cycle square wave (described at ) or you can generate DC on the main output if you hold the DDS in reset and set the signal offset to the value you want (described on the same page). Calibration would certainly be most welcome but as far as I know there isn't any implemented yet. I do plan to improve that, but I can make no promises as to when will I get any of it done. Also do keep in mind that basic resolution won't get any better any time soon - thousands of millivolts divided into 256 steps just doesn't get down to 1mV level (unless you de-solder that DAC and solder in a 12-bit replacement)...
 - https://github.com/arachnidlabs/tsunami-arduino/wiki/Reference#enableAuxiliaryFiltering
Blinkenlight has everything right. In principle you can even use the trim DAC to do arbitrary waveform generation, though doing so at any speed will require bypassing the high level libraries and the overhead they impose.
Thanks for the replies gents,
I am trying to generate dc signals within 0.1v, but what I could manage to get is 0.5v or 0.4v off. Using the provided “AUX” example in the tutorial, I get a noisy signal 300 to 400mv pk-pk ripple. However using the main output gives a much cleaner signal but with 0.5v error. Also on main output I can’t go full scale i.e. 5V (or 4.9 v), highest I could get was about 3v. Is it because I am doing it wrong or they supposed to be like this or else I have a bad board?
The aux port isn't really designed for clean signals; you're definitely better off using the main port. You should be able to calibrate out the offset - just determine what it is and subtract it from the value you output.
You can't get to 5V because the Tsunami isn't specified for that - it can do +-3V (a little more, really) for 6V total peak-to-peak.