synchronised USB

[Peasoup]

According to USB data acquisition faq, it is possible to connect multiple USB devices to a PC.

- should note USB acquisition is still new to me -

If this is true, and 2 devices (6015s for example) were connected, how could the acquisition of these dev ices be synchronised without a rtsi cable etc. as you would for PCI devices?

for ref, I use LV7

cheers

A

[Kenny_K]

You would just have to have the VIs that control the aquisition in the same loop so that they both started at the same time.  This would mean that you would need a Create Task, Create Channel, Read/Write, etc for each device and in the same while loop (or sub VI) and it should run both in parralell, syncing them.

Or you could use one main while loop and 2 loops in parallel inside it.

I put both ideas in the same VI, so it prob wont function normally, but you can copy part of it to a blank VI and try running it with the "Lightbulb" button (Highlight Execution) on so that you can see them running in parallel.

If you ahve any more questions, please post them.

Kenny

[Stuart_R]

There isn't any hardware facitlity for sharing clocks/triggers between devices such as RTSI and you will have to rely on software techniques as mentioned in the other comment, but this isn't going to be as accurate. In all honesty, if you want to synchronise between devices, USB wouldn't be the best option and I would recommend going down the PCI route instead.

[Peasoup]

Hi

Thanks for the responses.

I couldn't see how synchronisation between devices would be possible, but wasn't sure if USB could do something particularly clever.

I currently use pci with rtsi and triggers/timing to synchronise - just wondered whether USB devices would give me some other alternatives for DAQ.

I agree I could control separate tasks within a loop, but the lack of control on when each task started would not meet my requirements.

Cheers

A