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Wiring a headphone jack

Discussion in 'Beginner Electronics' started by Shrek, Jun 30, 2004.

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  1. Shrek

    Shrek Guest

    I have an old metal detector that has speaker only for output.
    It makes constant noise as there is no discrimination knob. I'd like
    to wire a headphone jack so my kids can detect with it without
    annoying everyone.

    I purchased Radio Shack 274-248 jack, and am looking for a schematic
    or instructions for how to wire it in. Obviously the speaker has 2
    wires, but the jack has 3 terminals. What wires go where?

    -??
     
  2. Don Taylor

    Don Taylor Guest

    Some jacks have only 2 terminals, you push the plug in and the tip
    connects with one of these while further back the barrel of connets
    with the other. But that doesn't switch between a speaker when the
    plug isn't in and the headphones when the plug is in.

    So, think of what you have as a switch. One of the terminals is
    for the ground side, that is going to connect to one side of your
    current speaker. Internal to the jack that is also going to
    connect to one side of your headphones. Next you have the audio
    that was going to your speaker, but you are going to slice that
    away from the speaker and route it into the second terminal. Then
    when the plug is in it will go out to the headphones. And when the
    plug is out it is going to come back out the third terminal and go
    back to the speaker.

    Now, there is a little diagram on the back of the package. Look
    for the terminal that connects to the little contact inside that
    touches the barrel of your plug. That's your ground. The other
    two contacts are going to be for what looks sort of like a little
    switch in the diagram. When you push the plug in it pushes the
    contacts and "changes the position of the switch."

    You can wire this up backwards, I did the last time I was doing
    this. The only bad thing would be if you shorted out the two
    wires that had gone to your speaker. When you first try it do
    something to make sure you should have sound and then just turn
    it on for a second, and then back off. Repeat with the plug in.
    If you just do this for a second you can probably tell you aren't
    hearing what you should be and turn off the power before toasting
    anything. Otherwise it is more likely that you will have it
    backwards and won't get audio to the head phones. If you happen
    to have a little ohmmeter you can try to check the connections to
    see if you have low ohms where it makes sense and millions of
    ohms when it should be open.

    And the little plastic case that the jack is built in, it doesn't
    do very well with soldering on the wires, realizing it is wrong,
    unsoldering the wires, resoldering them, etc. The plastic melts
    if you aren't careful. But a little caution should be enough.

    See if you can compare this to what you have and how much of it
    matches up.

    If you still have questions then throw me mail
    (address is valid)
     
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