Re: Image acquisition + motor control via USB port

Dave,

Thank you very much for your answer.

About your second possibility, I've actually tried even worst in
terms of speed in my loop: I've tried creating the vid object and
deleting it at each acquisition. It doesn't help!

As for the first possibility, even though it solves the problem (I
had tested it before), I'd like to avoid it: actually the two
components are plugged on an external USB hub with independent
powering, so that the PC doesn't have to provide power to the devices
(autonomy matter). I'd like to maintain this feature...

In case it would help, the devices' models:

Motor controller : 8SMC1-USBh from Standa
Video card : Grabster AV250 from Terratec
Hub : TU2-400 (4-port Hi-Speed USB 2.0 Hub) from TRENDnet

Any other clue?

Thank you already.

Regards,
Michael

Dave Tarkowski wrote:
>
>
> Michael,
>
> I think the problem is that the camera is taking all of the
> available
> USB bandwidth, or enough of it, so that you can not communicate
> with the
> motor. The camera is actually sending data to MATLAB from the time
> you
> call START until you have acquired the last frame of the last
> trigger.
>
> I can see two possible workarounds. The first would be to put the
> camera and the motor controller on different USB busses. Many PCs
> actually have two seperate USB controllers to increase the amount
> of USB
> bandwidth available. The only way to know would be to read the
> detailed
> specifications of your computer and figure out which USB ports map
> to
> which controller.
>
> A possibly easier solution would be to modify your code so that the
> camera is not continuously sending data back to MATLAB. Instead of
> using manual triggers and modifying the TriggerRepeat property,
> just try
> calling START right before you call GETDATA. This will make your
> loop
> run a little bit slower because the camera will have to be
> initialized
> on every run through the loop, but the USB bus will be free at all
> other
> times.
>
> -Dave Tarkowski
>
.

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