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help with simple question needed

Discussion in 'Electronic Basics' started by Beowulf, Feb 2, 2004.

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  1. Beowulf

    Beowulf Guest

    I just built the gaussmeter from plans at
    http://my.execpc.com/~rhoadley/magmeter.htm
    I am just a newbie, and know little about electronics.
    Two questions for anybody that can help me:
    (1) Is there any way to increase the sensitivity of the gaussmeter
    perhaps by putting two of them in series or something?
    (2) Is there any way to build my own gizmo to input this into my
    laptop computer serial port? I found a gaussmeter probe that hooks
    into a laptop serial port, with basic software to write comma separated
    value data values, and even this costs $500. I would like to build my
    own such setup if possible to collect magnetic field info in real time.
    ~Randall
     
  2. CFoley1064

    CFoley1064 Guest

    (1) Is there any way to increase the sensitivity of the gaussmeter
    Hi, Randall. Two questions, two answers:

    1) I'm assuming you are using the Radio Shack sensor. That one (Allegro 3515)
    has a sensitivity of 5mV/G. You might want to special order the 3516 mentioned
    in the app note. It has a sensitivity of 2.5mV/G. However, I'm not sure
    that's your problem. You've got a sensor that has a "zero" output of around
    +2.500V, and you want to detect small differences from that "zero". The way to
    do this is to use a voltage offset. Here's the easiest way to do this (read in
    fixed font like M$ Notepad):


    SW1 ____
    _/ | |
    .-o/ o-.------|7805|----.-------.-------------.
    | | |____| | | .---o---.
    | | + | | + | | | +
    +| ### | ### | | HE3505o-------o
    --- --- | --- | P1 | |
    - C1 |10uF | C2 |10uF .-.10K '---o---'
    9V | | | | | |<---. | DVM
    | | | | | | | |
    | | | | '-' | |
    | | | | | '-------------------o
    | | | | | | -
    | | | | | |
    '-------o--------o-------o-------o-------------'

    By using a 10K pot (preferrably 10-turn if you can scrounge one), you can set
    the pot wiper so there's no differential voltage between the pot wiper and the
    sensor output when there's zero gauss. That will allow you to put your DVM on
    the 200mV range instead of the 20V range, which is probably the main reason
    you're dissatisfied with what you're getting from the sensor. 5mV/G is really
    pretty sensitive for one of these things.

    2) If you're interested in a cheapie kit that will do what you want, you might
    want to look at the GP-3 PC I/O Board Kit from al-williams.com. It's based on
    a PIC, and gives you 8 general purpose I/O lines, 5 ea. 10-bit A-D conerter
    pins (5mV/bit), and a lot of other good stuff. It's based on a PIC, and the
    kit is only $40.00. You won't have any trouble reading the above circuit with
    the GP-3, and getting it in to your PC from the serial port. They even give
    you sample programs and source code in the languages of your choice, as well as
    the serial protocol if you want to roll your own.

    http://www.al-williams.com/gp3.htm

    Good luck
    Chris
     
  3. One way to simplify things and still save a bit of cash is to use a DMM with
    an IR or RS232 PC link. For well under $500 you can get datalogging and
    probably some features that would simplify your circuit and solve your
    sensitivity problem.
     
  4. Beowulf

    Beowulf Guest

    I am pretty naive regarding all this stuff-- basically the gaussmeter I
    built works, but I only see changes in the output voltage when a magnet
    comes within maybe 4 or at most 6 inches of the Hall Effect component. I
    would like to detect electromagnet signals several feet away -- is that
    even possible with a home-built gaussmeter?

    BTW thank you for such a nice reply, I am still looking at it as like I
    said I only know basic electronics, though I did build and solder some
    simple electronics projects as a teenager.
     
  5. Beowulf

    Beowulf Guest

    ..
    The only pot I know is the kind I used to smoke (smile) or the kind I
    cooked my spaghetti in tonight! Can anybody translate? Pot? Pot wiper?
    DVM -- can I buy a vowel???

    So you are saying that for about $40 I can built something to be able to
    input voltage signals e.g. from a gaussmeter, including some primitive
    software? That would be outstanding-- $500 for a commercial product just
    is outside my budget for what I have in mind. Electronics always seem
    overpriced to me as there always seems to be next to no components
    inside the box.
     
  6. Doug

    Doug Guest

    DVM =Digital Volt Meter
    Pot = potentiometer i.e a varible resistor with a connection at each end
    plus a third contact that can be moved. usually by turnning a knob. A
    volume control is an example.
     
  7. JeffM

    JeffM Guest

    Pot? Pot wiper? DVM -- can I buy a vowel???
    Well, maybe someone can--but if you don't understand the shorthand for
    variable resistor and digital voltmeter, it might not be you.
     
  8. CFoley1064

    CFoley1064 Guest

    From: Beowulf
    Probably not -- the effect decreases proportionally to the square of the
    distance, and that's quite a distance, unless you've got quite a magnet.

    Possibly you could tell us a little more about what you're trying to do? There
    are other ways of sensing from a distance. Retroreflective opto comes to mind
    -- in an industrial environment, that's usually a first choice.

    Good luck
    Chris
     
  9. CFoley1064

    CFoley1064 Guest

    From: Beowulf
    In your first question, you were asking about a kit. I assumed a little more
    knowledge about electronics than you have -- that's OK. A pot is a
    potentiometer, which is the variable resistor you use, for example, as a volume
    control. As you turn the dial, you increase or decrease the resistance. If
    you're setting this thing up on a perfboard or solderless breadboard, you
    should use something like the Radio Shack Cat # 271-343, which is a 15-turn, 10
    K ohm potentiometer which is available for $2.49 USD.
    Again, revising the answer to your level of knowledge and experience, you
    probably should go with the advice of another respondent, and use a DVM
    (digital voltmeter) for input. Many meters have built-in RS-232 output, and
    also have software included which will allow you to just plug it in and chug
    away (plug&chug). A good choice for a newbie would be the Radio Shack Cat. #
    22-812, on sale at all stores for $59.99 USD. Included with the meter is some
    elementary software which will allow you to get unattended data collection.

    That will do it, in and of itself, for a total newbie. If you have trouble
    hooking things up or getting it going, you should be able to ask anyone with
    any technical background -- it's pretty simple. If you have questions about
    the data collection software, the manual is on the disk.

    Good luck.
    Chris
     
  10. Beowulf

    Beowulf Guest

    Hey thank you so much. I ordered the GP-3 PC I/O Board Kit from
    http://www.al-williams.com/gp3.htm for learning to collect data into a
    serial port, and I am going to get the Radio Shack parts, pot, and DVM
    with software that you suggest. Lots of toys to play with! I will
    probably be back here in the near future with a few questions. I have
    soldered a pot in my distant past (I recall building an electronic
    mosquito repellent, etc.), soldered resistors, even taught basic physics
    of ohms, etc. But I really have little practical experience building
    this stuff. I have even done a fair amount of computer programming (C++,
    java, BASIC) in my past, so hopefully I can play with custom code to
    control the analog to digital data acquisition.
     
  11. CFoley1064

    CFoley1064 Guest

    From: Beowulf
    Start out with the Radio Shack DMM and the schematic with the 10K pot -- that's
    the easiest, and will probably get you close to the best results you can get on
    a hobbyist level.

    Good luck.
    Chris
     
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