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Audio switch project.

Discussion in 'Audio' started by vr4Legacy, Sep 26, 2011.

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  1. vr4Legacy


    Sep 26, 2011
    I am working on building an audio switch for my car that will allow me to hook my XM input and my iPhone (both 3.5mm) and switch between them on a single 3.5 mm output. I have seen plans and understand how to make one with a 3PDT switch.

    I have found several inexpensive 3PDT toggle switches, however I would prefer to use a rocker switch so it looks cleaner. I can't find one for less than $15-$20, and since the point of this project is to avoid paying $30 for a prebuilt switch, I don't want to go that route.

    If I understand how a 3.5mm plug works, there is a left and right channel and a ground.

    The diagram I saw switched all three between the two, hence needing a 3 pole switch.

    My question is, could I share the ground between the 3 at all times, and simply use a DBDT switch to swith the L&R Channels? Would this create a ground loop?

    Also, is there an inexpensive 3PDT Rocker switch that I just can't find??

    Lastly, how hard/expensive would it be to make the switch load sensing, hence automatic?

    Thanks for any help!
  2. shrtrnd


    Jan 15, 2010
    You may have to check a few, but auto parts stores should carry what you need.
    (Or a place that caters to truckers)
    People are big into doing what you're doing, and the demand at auto/truck places is high.
    (RV repair/modification vendors also)
    I got my last batch (years ago) of rocker switches from Radio Shack.
    Your only problem should be finding the finish on the switch you want to match your vehicle.
    $5 should be reasonable for a rocker switch. (but you can buy a Rambler or a Mercedes Benz type).
  3. vr4Legacy


    Sep 26, 2011
    thanks for the reply shrtrnd, as for finish, I could really care less, it's going in my console, msot I see are black (which is fine) I'll paint if it need be, I just don't want a toggle that could get caught on something.

    I'll keep looking. Do you happen to know if using a DPDT switch and sharing a ground will work? I'm really having trouble finding 3PDT Rocker switches.
  4. shrtrnd


    Jan 15, 2010
    Sorry, I'm not up on these new-fangled communications power requirements.
    Typically, the vehicle chassis is the car battery ground.
    For the new high-tech comm gear, there may be special power filtering (you know, to
    keep alternator noise and etc... off the power line.)
    If your question is about the switch itself: DPDT IS two separate circuits. I'm not sure
    about your reference to 'sharing a ground'. (Why you think you need a 3-Pole switch)
    I'm hoping somebody who knows about XM Radio and iPhones is going to jump in
    here and give you more exact information.
    I keep thinking that your problem CAN'T be unique. That other people have the same
    issue. And that being the case, there's a market for the switch you need.
    If car, truck, RV elec parts suppliers don't have what you need. There are a lot of
    on-line elec parts suppliers out there:
    Parts Express, Crutchfield, Jameco, MCM, All Electronics Corp, ....
    (Whoops, if you're not located in the States).
    Sorry I don't have your exact information, but hopefully you've got a little more information
    now, and somebody else might post a more useful reply.
  5. davelectronic


    Dec 13, 2010

    Why not use a SPST or DPDT and use a relay lots of contact arrangements on them, some relays for that could be small.
    Dave. :)
  6. vr4Legacy


    Sep 26, 2011
    Thank you, you've been very helpful. As for the 'sharing a ground' I don't have a better term. But essentially, if I understand correctly, a 3.5mm plug has 3 leads, a L,R and Ground. I wasn't sure if any interference would transfer across if I simply joined them together from each input across to the output.

    I understand the chassis is the ground, but with electronics and low level outputs, a ground loop is easy to create.

    Thanks again for your help.
  7. vr4Legacy


    Sep 26, 2011
    Never thought of it to be honest. Good idea!

    I'll see what I can find out.
  8. vr4Legacy


    Sep 26, 2011
    Here's a quick schematic.

    My only fear is that this will cause some interference running the audio through an energized relay. Any thoughts?

    I found some info online that says it's ok to use a common ground. This schematic is to wire an led for each side.

    Attached Files:

    Last edited: Sep 26, 2011
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