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using a coil and magnet to power an LED

Discussion in 'Electronic Design' started by Mike Pinch, Feb 26, 2006.

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  1. Mike Pinch

    Mike Pinch Guest


    I am interested in using a coil and a moving magnet to briefly light up an
    LED. I have only a basic understanding of electronics.

    Does anyone have any advice on what parts or circuit I would use to
    accomplish this?


  2. DaveM

    DaveM Guest

    Ummm Err... Ahhhh Is this a trick question???
    Really, the LED, coil and moving magnet are the only things you need, if the
    magnet is strong enough and the coil is large enough and the movement is fast
    enough. Can you elaborate a bit more on the specifics of your project, or is it

    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the

    Never take a laxative and a sleeping pill at the same time!!
  3. I would try a coil and a moving magnet.
  4. amdx

    amdx Guest

    Hi Mike,
    I'm sure you have seen the flashlights that you shake back and forth,
    a magnet to slide inside of a coil. These flashlights store the charge in a
    while your not shaking it. Is this the idea your after?
    Would a rotating coil and a stationary magnet work for you? Go to Radio
    and get a small DC motor, connect the LED to the motor with the correct
    and then spin the motor, the LED should glow.
    Give us a better idea of what your after.
  5. or a moving coil amd a magnet?

    seems to work in LTspice

  6. John Larkin

    John Larkin Guest

    Wind a couple/few hundred turns of small-gauge wire around maybe a
    toilet-paper cardboard core. Use maybe #30 enameled magnet wire.
    Connect it to the led or preferably to a pair of leds connected

    Drop a super-magnet, like one of the rare-earth things from an old
    hard drive, through the hole, the faster the better. The led's should

    More fun: drop a supermagnet straight down inside a long hunk of 3/4
    inch copper water pipe. Release it and quickly look down the pipe as
    it drops.

    I recently tried dropping a quarter down the bore of a megabuck
    superconductive magnet, expecting the eddy currents to slow its fall.
    It never came out the bottom, not because of the field but because it
    jammed in a flange halfway down. Very embarassing.

  7. Yabbut, the OP is not interested in that.
    I bet ;)
  8. You win,I lied. I couldn't find a symbol for a hand waving a coil (or

  9. Fred Bartoli

    Fred Bartoli Guest

    Did you put that nice zero threshold bridge, so that it lights whatever the
    direction you move the magnet.

    And with a transformer, if you suffer from Parkinson's disease you could
    make yourself a powerless christmas tree.
  10. John_H

    John_H Guest

    Take the guts out of this:

    and you have what you need. Moving magnet, coil, LED, let there be -
    shake shake shake - light!
  11. Matt

    Matt Guest

    Another cute experiment is to create a "motor-generator" from a couple
    of DC "muffin fans" like those used to cool computers. You connect the
    leads of the first fan to an LED/series resistor combination (keeping
    the polarity correct), and then you connect the leads of the second fan
    to its proper power source. The second fan will start spinning. Now,
    place the first fan close to the second one so that its airflow turns
    the blades of the second fan. As the second fan turns, it generates
    electricity to light the LED.

    Anyone remember those old 28 VDC motor generator sets used to power
    portable World War II electronic field gear?
  12. No. You just model the coil and magnet in spice and then pick up the PC
    and shake in back and forth, just like one of those flashlights.
  13. ehsjr

    ehsjr Guest

    Elegant! I would add a LED to that.

  14. Mike Pinch

    Mike Pinch Guest

    I just got back. Thanks for the feedback.

    The application isn't really classified in the sense that I'm not planning
    on putting LEDs into a stronglink or anything but there are some geometrical
    constraints which will mostly impact the coil. Any standard LED will fit
    into the space I have. The intent is to have the LED flash briefly but
    intensely. The coil needs to fit in a fairly narrow space so it needs to be
    "flat" (as in probably occupying less than 1/4 inch thickness) . The coil
    can be long. Let's say we had a long thin coil with lots of windings.

    If there is a long slender coil (say 4 inches long wrapped around an 1/8"
    diameter mandrel) with the proper number of turns, does the influence of the
    magnet (which is let's say 1/4" diameter x 1/10" thick) become
    time-dependent? Will the induced current gradually build up as this magnet
    traverses along the coil? Are additional components needed in this case?
    Remember, I am looking for a briefly flashing LED -- no constant output

    Also, I am messing around with various coils, chokes and wal-warts. Some of
    these devices seem to have a metal mandrel, some don't. How do I know what
    kind of mandrel (core) to use?



  15. Christopher

    Christopher Guest

    Hello Michael,

    Just when I thought I had it you changed rules.

    Actually one method is using three small button type batteries and a
    super bright LED. Make certain the LED forward voltage is under 4
    volts. Kids tennis shoes use this method. Look around in the toy
    section Walmart, I found packs of three 1" plastic marbles for $3 with
    a built in flashing IC chip, circuit board, four colors super brite
    LED's and the three batteries. That's for each marble!

    This triggers from a small spring switch that senses a mild impact.

    Trying to achieve 4 volts off of a very small coil and magnet seems a
    bit challenging.

    I don't think you mentioned what triggers your LED, physical motion?

    * * *

    Temecula CA.USA
  16. Mike Pinch

    Mike Pinch Guest


    Excellent feedback; thanks.

    I didn't want to use batteries in this application. The application is such
    that human intervention to change batteries is undesirable.

    Here's a question -- does a coil necessarily need to be wound in a circular
    fashion (cross section) or could a coil be wrapped around say a flat piece
    of something (like a popsicle stick)?

  17. Pooh Bear

    Pooh Bear Guest

    Like this ?

  18. Lukas Louw

    Lukas Louw Guest

    Our 20 month old has sneakers with a couple of LEDs on them that flash when
    she walks. I assume there is a coil with a loose fitting magnet in the
    shoes. Let me see if the wife kept the older too small ones, and I'll cut
    them open to see what's inside...

  19. Fred Bloggs

    Fred Bloggs Guest

    A battery...
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