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Measuring an external voltage on Mac

  1. Oct 21, 2010 #1
    I'm trying to help my 6th grader measure and graph the amount of power (eg voltage) her hamster will put out running all night long on it's wheel that is connected to a small DC generator. I am hoping to not buy an expensive DAQ and software. Does anyone have any ideas how I can do this on without spending a lot of money? Thanks for the help.

    Scott
     
  2. jcsd
  3. Oct 22, 2010 #2

    MATLABdude

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    Welcome to PhysicsForums!

    If you have programming and electronics experience, you can rig up a microcontroller (or Arduino kit or the likes) to transmit A/D (analog to digital) values back to a PC using USB or a serial port. If not (and you need it quicker than not), you can probably find a DMM with computer output (and logging software) for not so expensive (less if you buy it used, from say eBay or the likes).

    It might also be worth it to call around to any tech schools (especially those that offer electronics or electricians training) or universities (which might have an engineering faculty) or even local electronics or robotics hobbyist groups to see if someone there might be willing to lend one of those.

    Good luck!
     
  4. Oct 22, 2010 #3

    berkeman

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    Welcome to the PF! I moved this thread to the EE forum to try to get more help.

    As MATLAB suggests, a cheap USB Digital Multimeter (DMM) might be the easiest way to go. Maybe others have ideas...?
     
  5. Oct 22, 2010 #4

    MATLABdude

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    Can't really vouch for these guys or the product, but their low-end model is only U$40 (and figure another $10-$20 for a RS-232 to USB adapter):
    http://www.multimeterwarehouse.com/computer.htm

    That popped up as a first result in a Google search for "USB multimeter"

    Doing the same at eBay brought up a few similarly-priced multimeters--some of which look like they plug in directly into a USB port (again, can't vouch for any of these guys or their products).
    http://shop.ebay.com/?_nkw=usb+multimeter&_sacat=See-All-Categories
     
  6. Oct 22, 2010 #5
    If you can somehow get an AC signal in the audio range you could use the regular sound input. I'm thinking a small alternator instead of a DC motor/generator, but I can't think of an example offhand....I wonder if a stepper motor would produce a pulse signal? I should try that....
     
  7. Oct 22, 2010 #6
    I second the DMM with data logging idea. Unless you've got an electronics background you really don't want to be messing with microcontrollers and mixed signal stuff when a DMM will do the trick. Here's one thats relatively cheap and has data logging.

    http://us.element-14.com/jsp/search/productdetail.jsp?SKU=45M5527&CMP=AFC-GBE14 [Broken]

    If you don't have at least a mediocre DMM lying around the house, nows a good time to get one.
     
    Last edited by a moderator: May 5, 2017
  8. Oct 22, 2010 #7
    Ok, since it's been at least 10 years since I bought a (surplus) DMM...I just have to ask:

    How do you know the one you linked will do data logging? I skimmed over the user manual on line and found one (1) reference to "data sending" which said, "Please see the accompanying CD". Nothing in any selection matrix or device spec indicates remote data capabilities. Is it now such a standard feature that it doesn't need to be mentioned?

    And:

    $159.67+S&H for "a mediocre DMM"!!!?? my god, I'm glad I got that surplus one when I did...


    In other news I tried my stepper motor trick and it indeed produces a lovely, actually kinda inductive-kicky, pulse that is around 80Hz at a quite respectable voltage level while twiddling the shaft with my fingers at perhaps the rate a happy-hamster might. The experimental object was a KP4-M4 100-step/revolution baby that I got for 99 cents...surplus again... and I just scoped out one phase.
     
  9. Oct 22, 2010 #8

    berkeman

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    Using the sound input is a great idea, schip! She may be able to just generate some number of clicks per hamster thing revolution, and pick those up from whatever interface is available. Would you normally get a wave output file or streaming data or something from the audio input? What programmatic interface would be the easiest for them to use?
     
  10. Oct 24, 2010 #9
    ohoh...programatic interfaces...I don't know what to recommend nor how sophisticated our OP is, or if they are even still lurking here....

    There are a number of audio capture and editing programs that might do something useful. On Widows there's "audacity" http://audacity.sourceforge.net/ (hmmm...seems to be a Mac version too). Using Java media extensions one can also read and manipulate audio and files. I'm sure there's some screwy Microslop C and/or VisualBasic access but I haven't looked at them in a long time.

    Presuming that the speed of the wheel varies the frequency of the signal one might do a spectral analysis and find some kludgy way to dump (probably text) data into Excel to do time series hacking.

    Oh, you know, another possibility is a wind-speed monitor. Didn't this sound like a simple straight-forward project when we started?
     
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