reversing voltage polarity

Discussion in 'The Projects Forum' started by Bub, Jul 8, 2008.

  1. Bub

    Thread Starter New Member

    Jul 8, 2008
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    0
    Hi,

    I have a wire that will output either a positive or negative voltage onto an LED, depending on the input. I need a way to change the negative output into positive voltage of the same magnitude (or as close as possible) so that it can power the LED. The circuit needs to be as small as possible. Any suggestions?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    You could use a fullwave rectifier (bridgecel) in front of the led.
    Here demonstrated with a sinawave input signal.
    http://www.falstad.com/circuit/e-fullrect.html
    Do mind the restistor to limit the led current.

    Greeting,
    Bertus
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    Use two LEDs, connected in opposite polarity.
    [eta]
    See attached
     
    Last edited: Jul 8, 2008
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you are using sgtwookies drawing you could also use a 2 pin duo-led.
    These duo-leds consist of two leds in different colors, connected opposite.
    In this way you can see if the voltage is positive or negative.

    See link (in dutch but the picture is clear).

    http://www.leds-buy.nl/pin-duo-led-groenrood-graden-5mm-p-84.html

    Greetings,
    Bertus
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Bertus,
    DuoLEDs will not work in this application. They have a common anode or a common cathode, depending upon the device; they have three leads.

    They may exist, but I haven't seen a trademark DuoLED where they are connected anode-cathode and cathode-anode.

    Radio Shack DOES sell a red/green bipolar LED that only has two leads, which would work just fine in this application. Link:
    http://www.radioshack.com/product/i...032058.2032233.2032298&pg=2&parentPage=family
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    In the link provided there are leds with anode connected to the others led kathode.

    There are green/red and green/orange available over there in 3 and 3 mm.

    Greetings,
    Bertus
     
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