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Sharing OScope and BOE on same USB Port — Parallax Forums

Sharing OScope and BOE on same USB Port

Jim McCorisonJim McCorison Posts: 359
edited 2005-01-15 01:17 in Learn with BlocklyProp
The USB oscilloscope documentation says that it should be the only device on a root level USB port. I understand that the issue is current consumption. Is it acceptable to combine both the Oscope and BOE on the same port using a non-powered splitter? The schematics for the BOE show that the USB-Serial converter components draw their power from the USB port.

My dev platform is a laptop and one more cord would certainly not be a welcome addition.

Thanks,
Jim

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2005-01-07 20:59
    The issue is not only current consumption but speed. A 'native' USB port (on the PC) runs quite fast (50 MBit/Sec? 150 Mbit/Sec? Not sure). All the ports on an un-powered hub run much slower (1.5 mBit/Sec).

    The easist solution to this is an additional PC card in your laptop with one to four USB ports. Note you will drain your laptop battery faster this way. A 'clunky' solution is a powered USB hub -- but you lose portability this way.

    If your laptop has two USB ports already, then one can be O'Scope and one BOE.
  • Jim McCorisonJim McCorison Posts: 359
    edited 2005-01-07 22:08
    allanlane5 said...
    All the ports on an un-powered hub run much slower (1.5 mBit/Sec).

    Well Belkin technical support begs to differ with you on that. Their statement was that there is no speed difference between powered and un-powered hubs. The only difference is that a root hub will provide up to 500ma to a device, where as an un-powered hub may provide as little as 100ma per device depending upon how many devices are placed upon it.

    He made an interesting additional comment regarding hub speed. According to Belkin USB 1.1 hubs, of any form, provide anywhere from 1.5 - 2.5 mbit/sec throughput. And that while the 1.1 spec is for UP to 12 mbit/sec, they have no hubs in their product line that will come anywhere near that.

    Now this is the statements of one tech support person at one company. But Belkin's products are pretty middle-of-the-road performance wise, so I would take this as indicative of consumer grade USB hubs as a whole.

    On the other hand, the tech person could be all wet. That's been know to happen in this industry before.

    Jim

    Post Edited (Jim McCorison) : 1/7/2005 10:22:14 PM GMT
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-01-08 00:16
    Well, perhaps. My Keyspan mini-hub (highly recommended) says with the AC adapter, it will power 500 mA to each port. Without, it only supplied 100 mA to each port. It does not mention the speed, so perhaps I've got that wrong. I did assume that the highest through-put would be to a powered port, though.

    I have not had good luck, personally with the Belkin USB products.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-01-08 00:46
    Allan,

    ·· For your info, USB 1.1 ports have a transfer rate of 12 Mbps/S, while USB 2.0 has a transfer rate of 480 Mbps/S.· As you can see (With a little math), USB 2.0 is 40 times faster.



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • Robert KubichekRobert Kubichek Posts: 343
    edited 2005-01-08 01:07
    turn.gif Check out htis link;

    http://www.everythingusb.com/usb2/faq.htm

    It's quite informative!

    yeah.gif


    Bob
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-01-08 02:15
    Hmmm,·a second look at my post makes me think it looks a little crass, which wasn't what I meant...I was just offering some specs since I am in the computer business!· smilewinkgrin.gif

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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • Jim McCorisonJim McCorison Posts: 359
    edited 2005-01-08 03:29
    Chris said...
    USB 1.1 ports have a transfer rate of 12 Mbps/S

    It should be pointed out that the USB speed is UP to 12 mbps/sec. Finding actual real genuine speeds of various devices is like finding hen's teeth. They all say they comply with USB 1.1, or USB 2.0, or some marketing buzzword that makes one sound like the other. But just try finding a published performance number.

    Jim
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-01-09 00:26
    Jim,

    ·· As a computer technician of 20+ years, I can tell you from experience that when you're doing something like backing up data to a USB Drive, you can certainly see the difference...I remembed I copied some commercial clips I did for a friend's business onto one of my USB 2.0 160GB HDs...It took about 1 minute...When I took it over to his house we realized he didn't have USB 2.0!· It took 40 minutes to copy the same files...In terms of throughput that confirms the difference in tranfer rate difference between the 2 standards...So I will go out on a limb and say yes, I am using the full bandwidth in that sense.· I guess the same thing with our Thumb Drives...We are usually moving a few hundred MB at a time.



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • Jim McCorisonJim McCorison Posts: 359
    edited 2005-01-09 00:46
    Chris said...
    In terms of throughput that confirms the difference in transfer rate difference between the 2 standards...

    Chris,

    I was referring only to USB 1.1 devices. Yes, 2.0 is mucho faster. But my statement about USB 1.1 devices still stands. There is little if any real data published by the various manufacturers. It comes down to "buy it and see". They claim compliance with the spec, but that's it. I've not looked at any 2.0 devices, but I'd be surprised it it was any different. Expect it to be a lot faster, but don't have a 1.1 device on the chain, or the whole chain degrades to 1.1 performance.

    Cheers,
    Jim
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-01-09 01:01
    Jim,

    · In the PC world it's a RARE thing that anything meets or compiles with a given spec!· =)· Look at Firewire...I've seen so many different companies creating their own version, when they all should be the same...Now I think most of the companies have given up using their own naming conventions for fear that people will avoid them thinking they are incompatible with the "standard."

    Your point is noted.



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • Jim McCorisonJim McCorison Posts: 359
    edited 2005-01-09 03:14
    It didn't use to be that way. There was a time (boy do I sound old or what) when specs were published by techies, not marketing, and you could decide what was the best to put in your system. Now PCs are marketed like microwave ovens to people that can't program their microwave oven either.

    That's where I find fun and enjoyment in the microcontroller / electronics world. The information is there for the asking. And there is more info than any one person could every assimilate.

    Jim
  • Jim McCorisonJim McCorison Posts: 359
    edited 2005-01-09 19:50
    Just an update on this. I went out and bought a cheapy non-powered USB hub. It says it's made by Compaq... but who knows. It was actually a couple bucks cheaper than the no name brands I found.

    So far, using the non-powered hub with the USB Scope and BOE has worked fine. I don't think I've really stressed either one yet, but working through the Understanding Signals course it has so far worked fine.

    Jim
  • Doug PientakDoug Pientak Posts: 16
    edited 2005-01-15 01:11
    The Parallax USB Oscilloscope draws about 220 mA of current from the USB cable.· Any one USB root should supply 500mA of current, if you go over the 500mA limit power could be interrupted or shut off completely.· Usually the mother board with shut power off completely until you reboot.· So the reason we asked to use the scope by it self is to prevent using it with another devices that·could draw a lot of current·shutting down the USB port.· The BOE draws less then 10mA and is fine to use with the Parallax USB Oscilloscope.· If you did want to run another device that draws a lot of current you could use a powered hub.·
    ·
    Also you don't need to worry about other devices using up bandwidth on the USB buss.· All the data is acquired in hardware and then when the buffer is full the data is sent up to the PC to be displayed.· Even at the fastest setting the Parallax Scope is only uses about 100Kbytes of the available bandwidth.
    ·
    At the moment we are developing new software for the Parallax USB Oscilloscope and if any one is interested in beta testing software feel free to contact me.· Also please send any suggestions you may have for the new software.·
    ·
    dpientak@parallax.com
    ·
  • Jim McCorisonJim McCorison Posts: 359
    edited 2005-01-15 01:15
    Doug,

    Thanks for the input. I am only using the BOA and scope on the single port. It's been running just fine with no problems. Which given the power consumption you mentioned is not surprising.

    Thanks,
    Jim
  • Doug PientakDoug Pientak Posts: 16
    edited 2005-01-15 01:17
    No problem.
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