As Lynn (johnsold) has been mentioning, the software-timed USB board you intend to use has some very serious limitations for the task you're looking to accomplish. I'll be even more blunt: it's tough to believe you'll ever be satisfied with the (lack of) speed and/or repeatability you'll be facing if you stick to using such a limited piece of DAQ hardware.
If you've got piles of time and absolutely no money you can conceivably make it work, but I think you're in for a long frustrating experience.
At the kind of pulse rate you can achieve through software alone, you will always be seeing the "ringing" transient of the steppers' single-step response. A stepper can easily overshoot by half a step or more as it vibrates into a final steady-state position. The period of vibration will often be in the single digits of msec, and any attempts to read an analog sensor during the vibrational response will have very poor repeatability. Once you limit yourself to the speeds you can achieve through software timed DO over USB, you'll actually need to slow the step rate down far more so that the vibration response damps out *before* you take the reading. That could easily be many 10's of msec.
I'd probably be wanting to do something like a raster scan where the AI sampling was synced to the step pulse commands. I'd probably want to sweep one axis in the same direction each time, and increment the other axis by one step during the return stroke when I wasn't taking AI data. I'd be trying to sweep at a fairly high speed, well above the natural freq of vibration. At some point, there'd be a need to calibrate the dynamic position error (actual position vs commanded position at the time of the step pulse & AI sample), but repeatability should be decent because at higher speeds, the position error (as measured at the instant of each step pulse) is fairly constant. The overall sweep could probably be done at least 50x faster this way.
-Kevin P
ALERT! LabVIEW's subscription-only policy came to an end (finally!). Unfortunately, pricing favors the captured and committed over new adopters -- so tread carefully.
