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3.5mm Headphone Jack LED?

Discussion in 'LEDs and Optoelectronics' started by ssniesle, Jun 5, 2012.

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  1. ssniesle

    ssniesle

    4
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    Apr 28, 2012
    Is it possible to make a LED flash with a standard 3.5mm headphone jack as the only power source?

    I was thinking that you would do the following:
    1) write a program that would maximize the output from the headphone jack.
    2) Use a bridge rectifier to turn the headphone jack from AC to DC.
    3) Use a transformer to bump up the Voltage to 1.7V
    4) Use a capacitor that will eventually light the LED

    Does this make sense and if so how would I calc the values.

    Thank you
     
  2. khankll

    khankll

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    Feb 6, 2011
    Transformers do not work on dc the only work on AC.
     
  3. davenn

    davenn Moderator

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    What is the headphone jack connected to ? presumably some sort of music source?


    D
     
  4. ssniesle

    ssniesle

    4
    1
    Apr 28, 2012
    iPhone to drive LED

    Khankll, yes you are right. I would have to transform the AC before converting it to DC.

    Davenn, i would like an iPhone to power the LED and have a custom song/app manipulate the output.

    I was also considering using a battery to drive the LED and connect the audio output to a transistor and use it as a switch....comments?

    thanks
     
    saad hnor likes this.
  5. BobK

    BobK

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    The second method is a lot better. I doubt that there is enough power in coming out of the headphone jack to directly power the LED.

    Bob
     
  6. Mongrel Shark

    Mongrel Shark

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    Jun 6, 2012
    It's almost do able.

    I just measured a headphone jack. 0.24v @10 micro amps.

    I know of joule thief's that will do one or the other but never seen one do both at once.

    Lidmotor's "Penny Ossilator" modified with a germanium transistor might do it.

    This one need's .5v but it's using silicon transistor...

    I am working on getting LED's to light off similar power levels myself. Been looking at germanium transistor data sheets for days.



    Please let me know if you find a good one that will run on low current. Best I can do is 700 micro amps from .2v

    If you can make a custom app. You might be able to push a few more micro watts.....
    [edit] You could get a lot more power if the device has a USB port

    Good luck!
     
    Last edited: Jun 6, 2012
  7. BobK

    BobK

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    Jan 5, 2010
    If your calculation is right, there is no hope.

    .24V at 10uA = 2.4uW

    Typical red LED 2.0V at 20ma = 40000uW = 40mW

    But I think it is wrong. A typcial headphone amplifier puts out about 50 to 100mW, which is enought to light even the ineffiecient LED above.


    Bob
     
  8. Mongrel Shark

    Mongrel Shark

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    Jun 6, 2012
    You could be right Bobk. I measured the output on my laptop, which is not the loudest headphone jack. I didn't feel like pulling screws out of my speakers and didn't have a jack to check it there. Although I would expect my laptop would be similar to an iPhone etc... Using an amplified jack seems like cheating..

    And I can light that led at 50hz from less than [email protected] with blocking oscillator.... So visible (very dim) light from .0005w or even less. I'd do a video, but I don't have any low volt led's. 3.2v is the smallest I have..

    I have a video up as of 12 hours ago. Where I light a 3.2v 20-40ma bright white led from less than .2v @ 800ua. So .16mw or 160uw... Transistor is less than ideal. running at over 7khz. if I can slow down the flashes. I can get more visible light from less power. Although my LUX meter can tell the difference, my eyes don't notice.. [email protected] was actually hurting my eyes...

    If you have 1mw or more. No reason you can't flash a led. If the flashing is supposed to be detectable by eye (ie less than 30hz). You could get a bit of brightness in a low power led...
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    I'd say it would be possible.
    You'll get twice the power if you bridge the left and right channels by driving the left and right outputs in antiphase, with say a 1 kHz sinewave or squarewave, and connect a transformer primary between the two signals.
    Use a turns ratio of around 1:20 or so, using fine wire on something like an RM5 or slightly smaller with a moderate permeability core, and rectify the output using a bridge with low voltage drop - you can use germanium or Schottky diodes, or an active bridge made from four MOSFETs (see http://www.irf.com/technical-info/whitepaper/TP-080527.pdf) if there's enough voltage, or perhaps just connect the LED straight across the secondary (with a small current limiting resistor, maybe) for simplicity.
    You can get red and green LEDs that light pretty brightly at just 1~2 mA forward current.
    Some trial and error will be required though.
    More details? Just ask.
     
  10. Ben144

    Ben144

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    Apr 15, 2016
    Hi Please help me, I have the same question. Does anyone know how this could be done? I was struggling with my neck injury, making circuits to do this but I dont know what I'm doing and suffered a lot. (car accident)
    Im trying to make a healing device that just outputs an audio signal as a LED oscillation.
    THanks
     
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    and how is that supposed to work ?
     
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