IC Relay for light to indicate headphones are on

Discussion in 'The Projects Forum' started by Bill.Roberts, Jul 25, 2013.

  1. Bill.Roberts

    Thread Starter New Member

    Jul 25, 2013
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    I have a problem at work of people starting to talk to me when I'm on the phone (computer based IP phone) or listening to music.
    I thought I could just use a splitter from the headphone jack of my computer, and use some kinds of IC realy to power a LED that I could mount to my monitor, so people can see if I'm on the phone before they start talking at me.

    Ideally it could or should be a latching relay that I could reset so the light doesn't go out if there is no quite spot in the music.

    I am familiar with 24V & 110V industrial controls, but have really no experience with this tiny voltage / current stuff.

    My questions are, would this even be possible off of a headphones jack?

    What IC relay would do the job?
     
  2. sirch2

    Well-Known Member

    Jan 21, 2013
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    Is there power on your headphone jack? If not you proabablt can't reliably use the audio to directly drive the relay, you will need some additional circuitary such as schmitt trigger.

    A two pole relay can self-latch. Connect one of the poles across the coil via a normally closed push button so that once the relay activates it is held in until the PB is pressed.
     
  3. Bill.Roberts

    Thread Starter New Member

    Jul 25, 2013
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    I was afraid it wouldn't be reliable. That's why I was thinking the latching would be good. I thought the ringing would be enough to latch in the relay, or some loud point in the music. It wouldn't need to be tied to the beginning of the first song.


    I am understand the workings of a A two pole relay, but I'm not sure what voltage / current you get from headphones, or what specific IC relay would be sensitive enough to be set.


    I have not heard of a schmitt trigger, can you explain a little more.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    What's different between your "stay away" mode and you're "c'mon in" mode? I mean, don't the headphones being on your head send enough of a message?

    A manual switch would be a simple option for you to implement.

    Controlling the light status off the headphone's audio signal is perhaps the hardest way to do it, but not at all impossible. For example my sound system's subwoofer automatically comes on or turns off depending on the signal it sees.
     
  5. Bill.Roberts

    Thread Starter New Member

    Jul 25, 2013
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  6. sirch2

    Well-Known Member

    Jan 21, 2013
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    A Schmitt Trigger basically turns an alternating signal into and on/off signal and can let you set the output voltage.

    I wouldn't know the voltage/current from a headphone jack but it seems likely it may be effected by the insertion if a relay. A bit over halfway down that wikipedia page I linked to is this diagram:

    [​IMG]

    This could pretty much replace your relay - you would probably still need some kind of latch but you could power it off the computer's USB port (5V).

    I guess you could just try the relay approach and see if it works.

    Another thought that just came to mind is you may be able to use a Flip Flop with a few other components. Because you can build one from a couple of transistors you can probably configure it for the signal levels you had
     
    Last edited: Jul 25, 2013
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