better help / tutorial on realtime instruments

Hi,

I'm trying to get aquainted with using instruments in a GUI to display signals logged on a realtime target machine. I have attempted to follow matlabs inverted pendulum example but am finding it to be very confusing... I would just like to get a sin wave streamed from my target machine to plot to an axis on a gui as a proof of concept but the only example available is for a complex applicaiton that I am having a hard time understanding. Admitedly, I'm new to using the app designer which isn't helping my comprehension, but I really think there ought to be a clear explaination of the process of implementing a realtime instrument object... Any advice is appreciated!

Answer 1

[Christopher Bitikofer]

Followup, I was able to get the an Instrument object working following some much needed calories and time spent tracing functions in the demo inverted pendulum app...

That said I think there should be a better explaination posted in the documentation walking users through, what a callback function for instruments should do, what the eventData object is, and preformance optimization... in my use case, I need the gui to at least maintain a steady framerate while playing back a signal from the target machine. Right now things are still pretty choppy... I would appreciate a way to set a target framerate...

[Walter Roberson]

You cannot set a target framerate. The only framerate control is "drawnow limitrate, which discards frames beyond 60 frames per second.

[Christopher Bitikofer]

That does seem to be the case. I'm finding the framerate performance to be pretty disappointing (it sort of looks like the app hovers at ~20fps but occaisionally lags noticably). My hope was to use a GUI to play a sound and display feedback to a user performing an experiment while interacting with a robot, but if I can't acheive a reliable latency between the target machine and the host, I don't think that trying to have a timer signal originate from the target machine will work...

The alternate approach is probably to let the host PC run the signal using a timer object and send it via an instrument to target... again I need to understand how much latency and how steady the latency between devices is, but I expect that way my GUI could at least run a consistant framerate...

[Walter Roberson]

Have you looked at Psychtoolbox ?

http://psychtoolbox.org/docs/PsychPortAudio

[Christopher Bitikofer]

I hadn't heard of that toolbox, but it seems pretty useful! Thanks for the idea I'll look into using it.

[Jon Lobo]

Hi Christopher (and anyone else who might find this useful),

I made an example for this workflow with a simple model and app that I thought might be useful (see attached).

-Jon