Max number of USBs?

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ctm
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Max number of USBs?

Postby ctm » Thu Dec 22, 2011 5:59 am

Hi there,

QUESTION
In the past I've found some OS (namely, Windows XP) have problems managing more than 12 USB devices.

1. Will the PhidgetsSBC2 have any issues managing 17 to 20 USB devices (using multiple hubs as required) assuming I give it the 2.5 Watts of power per device as mentioned in the specs?

2. Otherwise, which would be the reasonable limit of USB devices for the PhidgetsSBC2 (using multiple hubs as required)?

SETUP DETAILS
I'm currently working in a project that involves reading from 32 Force Sensing Resistors (4 Flexiforce and 28 Interlink) and 28 strain gauges.

- For reading the Force Sensing Resistors I plan to use four 1018 I/O Phidgets boards (each I/O board has 8 analogic inputs hence 8 boards * 4 inputs = 32).

- For reading the Strain Gauges I plan to use thirteen 1046 4-Input Bridges using wheatstone bridges (each bridge has 4 inputs hence 12 bridges * 4 inputs = 28)

Instead of running 17 USB cables to the computer I thought of using the 1072 PhidgetsSBC2 with three 4-ports USB hubs and put everything into a box and simply running a long ethernet cable to the computer.
ctm

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burley
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Re: Max number of USBs?

Postby burley » Thu Dec 22, 2011 8:17 am

The theoretical maximum for the number of devices connected to the USB is something like 127. 20 devices should not be a problem provided, as you say, they get the power they need to operate normally.
Brian Burley
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ctm
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Re: Max number of USBs?

Postby ctm » Thu Dec 22, 2011 8:48 am

Sounds good enough.

Have you ever made any test with the 1072 PhidgetSBC2 connected to 20 USB devices or more?
ctm

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burley
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Re: Max number of USBs?

Postby burley » Thu Dec 22, 2011 9:14 am

To my knowledge we have never tested it on the SBC before but we did have a person a while back who had 300 1063's connected to a single PC.

http://vimeo.com/10626181
Brian Burley
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Patrick
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Re: Max number of USBs?

Postby Patrick » Thu Dec 22, 2011 9:58 am

While I'm sure it will work, I'm not sure how well the webservice will handle pushing all the data from 17 phidgets over ethernet. You may run into latency issues, depending on your chosen data rate / sensitivity and the stability of your data.

-Patrick

ctm
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Re: Max number of USBs?

Postby ctm » Thu Dec 22, 2011 10:41 am

The data is to be used for a real-time animation, so the intention would be to read values 30 times per second (to achieve a framerate of 30).


If the web service is not fast enough my alternative would be to write a
simple program for the SBC that:

1. Keeps up with all the sensors, i.e. it registers for its events and locally stores the latest value for each them.

2. Listens on a given port for incoming connections.

3. If anybody connects to that port it starts pushing to them all the locally stored sensor values every 33ms (30 times per second) .

4. I would use Java sockets in order to communicate since I believe it should have little overhead (C sockets might even have less overhead, but if I'd rather use Java for network communication if I can get away with it).

Do you foresee any problem with this solution?
ctm

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Patrick
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Re: Max number of USBs?

Postby Patrick » Thu Dec 22, 2011 12:26 pm

You should be able to get 30 events per second without problems.

Another alternative would be to get a high-quality USB extender.

-Patrick


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