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Activate tiny RELAY by headphone jack?? (PLEASE HELP)

Discussion in 'General Electronics Discussion' started by supak111, Apr 29, 2012.

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  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I think there would be plenty of power there, harnessing it in a sensible way is a bit of a challenge. You can probably live with an average power consumption under a milliwatt.

    I might charge a small capacitor (say 1uF) and use it to power a Schmitt trigger which extends the pulses it receives (essentially straight from the audio). the output is used to switch a mosfet. If this is isolated with a transformer, it should operate as a switch.

    The interesting behaviour would be during power-up. As the capacitor discharges, the mosfet will already be off and presumably the Schmitt trigger will have control of its outputs until the capacitor voltage drops below Vgs(th)

    it might fail the OP's idea of "simple" though.
     
  2. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    There is nothing on the market that can do this already? Even if it uses an external power. Can anyone think of anything that could work that I could just buy?

    I was able to modify a 12v clapper relay to work but they are just not practical: its too expensive, I have to modify it, and it uses an external power.

    Would it be possible to use 2 mosfets? 1 to amplify the sound out of the mp3 player, and second on as a switch?
     
  3. CocaCola

    CocaCola

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    Apr 7, 2012
    As I suggested on page 1, a LM3915 VU meter circuit could be hacked to do what you want... There are DIY LM3915 kits out there, all you would need to do is interface the relay to one of the outputs... As I stated before it's not the creme of the crop solution but it's one that is simple to get working and understand...
     
  4. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    Yea that VU meter looks like something I will try, I must have missed that post on the first page sorry.
     
  5. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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  6. QuantumCheese

    QuantumCheese

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    Apr 27, 2012
    If were now opening it up to including external power, it becomes quite simple
    so yes, probably, with a bit of hacking about.
     
  7. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    Doesn't look like I'm not gonna make it work easily without the external power so I'm just looking for cheap alternatives.
     
  8. Lenp

    Lenp

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    Sep 8, 2009
    Don't complicate it!
    Use a small audio transformer to step the audio voltage up, then use a sensitive gate triac to switch a low voltage AC relay or optical isolator. Parts cost only a few dollars. I've used a similar design in over a thousand produced units. I can supply details if needed! PM me...
     
  9. supak111

    supak111 ★ƃuᴉɯǝɥɔs sʎɐʍlɐ★

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    Apr 29, 2012
    I'm not trying to complicate it.

    Problem I had was that I was only able to get .07V for the speaker wires, not enough to get the transistor ON. But I ended up make the sound produce .9v so I was able to use just 1 transistor. Ended up being super easy and super cheap.
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    This is my first post here and I'm surprised to see that absolutely no one was curious about what it is that you're switching. So, I'd like to be the first to ask.
     
  11. wdancer

    wdancer

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    Mar 12, 2010
    Yeah, if you are doing it to turn off your speakers when you plug in your head phones, it is pretty simple.

    3.5mm audio jack with internal switch in series with the coil of the relay and a small power supply (old wall plug power supply). You are not going to get away from using a power source for your circuit since you need a voltage to turn on your relay.
     
  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    What makes you think that's what he wants to do? Nothing the OP posted even remotely hints at that. The OP is obviously triggering something.
     
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