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Electronics Making an "audio switch"

Discussion in 'Modding' started by woof82, 5 Jul 2012.

  1. woof82

    woof82 New Member

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    Hey all,

    I really wanted some kind of box on my desk that I could use to quickly switch between my headset, headphones and amplifier so I could select my audio output without having to rummage around behind my computer plugging things in.

    So I had this idea to have a box with one female "input" socket and three female "output" socket all for 3.5mm jacks. A rotary switch in the middle could be used to select which output was activated.

    At first I thought "simples" I can just use a 3P3T switch and wire it all together. Most basic solution. TBH I don't know how 3p3t rotary switches work, so I don't know if this is possible.

    Then I thought it would be cool to have indicator LEDs to show which output was selected. I think maybe this requires some transistors but I have never used a transistor in my life and don't really know how it works.

    So here I have made a (draft) circuit design using a battery to provide a voltage to the gates of the transistors, indicator LEDs not included. I think in reality it will be more complex because it would be in stereo.

    Is this a good solution? What kind of transistors would I need? BJT/Mosfet/pnp/npn?

    [​IMG]
     
  2. Technobod

    Technobod Finally bought a desktop :D

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    A 3P3T switch is by far and away the easiest way to do it but wiring it up could be 'interesting' and they're not cheap. I think the cheapest way to do it is 3x 3PST switches with the symbol http://www.tedss.com/Switches/pictures/3PST.gif this would allow you individual switching on your outputs so more than one could be on at once (if that would ever be useful?)
    Obviously on one side you have your input connected to all three swithces and then one output per switch on the output side.
    Adding an indicator is imho unnecessary and would make it more expensive and complicated but just make the switches 4PST and on the fourth pole have a simple power-resistor-led-switch loop which will illuminate whenever the switch is on.
    Hope that helps.
     
  3. Technobod

    Technobod Finally bought a desktop :D

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    I just knocked up this, obviously only two outputs (image got cropped :grr:) this includes the indicators as well if not just make the switches smaller and my program doesn't have 4PST switched so just imagine they pairs are connected.
    [​IMG]
     
  4. geebles

    geebles Own's a Dremel

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    A much simpler solution would be to use 3x 2pole switches (those small little black ones on everything)

    1. Link all grounds together (ground on audio in, and ALL audio outs)
    2. For each of the switches, connect the audio in L to the left centre pin, and audio in R to the right centre.
    3. Each switch is now going to 'turn on' each of your audio outs, so for each switch, wire the audio out L to the top left pin, and audio out R to the top right pin.

    So now with ALL switches off, you will hear no audio, and each switch on controls the device, so using this way you could turn them all on and hear audio out of all of them!

    Not as fancy as a rotary switch, but its VERY cheap, and requires no transistors.. ps the circuit you drew above will not work, you have not added any ground and you have wired all the RIGHT channels together.. you'd need 2 transistors per audio device for left and right channel. I don't think transistors are the best as the current will be limited and i'm sure there is some resistance in them so it will not be clean.

    If you want to have everything you want, use a rotary switch with a transistor to power a 2 pole relay. 2 pole because you need 2 channels.. you can also put an led in this idea.. BUT this is the most expensive as you'd need a switch, 3x relays and 3x transsitors (you could probably do it without the transistor but there would be lots of current going thru the switch all the time)

    Hope that helps a little bit!

    G

    EDIT: I meant the OP circuit, not the circuit Technobod posted! :)
     
  5. Lance

    Lance Ender of discussions.

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  6. Technobod

    Technobod Finally bought a desktop :D

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    Geebles is completely right you do not need switched grounds so my circuit is far overcomplicated, the switches can go down to 2PST for no indicator light or 3PST for indicators included.
     
  7. woof82

    woof82 New Member

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    Excellent, thank you for all the help guys! I've ordered some 3.5mm sockets, a couple of rotary switches and bunch of 3PST switches off ebay in case the rotary is not suitable. I'll have a play when they arrive, then I can think about designing the box and getting some LEDs ^_^

    Maybe if I'm feeling adventurous I can see if I can power the LEDs from USB... :p


    I figure it is possible to buy something to do this job, but what you linked has component audio instead of stereo 3.5mm jack. It is more easy for me to have 3.5mm sockets. Also if I make it myself it is fully customisable and more fun :)
     
    Last edited: 5 Jul 2012
  8. Lance

    Lance Ender of discussions.

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    If you get this working I might have a go myself. I'm in the "I hate unplugging and plugging stuff in" catergory aswell.

    However just as a heads up, component audio is stereo audio, they are just different sockets, I run on of these to swap them over. But mod on amigo!
     
    Last edited: 5 Jul 2012
  9. woof82

    woof82 New Member

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    Thanks I will post a guide if it works out. Of course yes component is also stereo but I did not want the faff of extra cables and connectors everywhere ;)
     

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