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Questions about building an RCA switchbox

Discussion in 'General Electronics Discussion' started by tizzdizz, May 31, 2016.

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  1. tizzdizz


    May 31, 2016
    Hi guys,

    I'm somewhat inexperienced as an electronics hobbyist, but I do have a number of other hobbies (music instruments, cars, general tinkering). I have some very basic questions that I was hoping you could help out with, so that I don't ruin all my stuff.

    I have an old stereo receiver that doesn't have many inputs that I want to be able to hook up my various stereo equipment/video game systems to, and switch back and forth without constantly reaching behind and plugging/unplugging RCA cables. I was going to buy a simple 8-port switch box from Amazon, but they look cheap and boring. I like creating things, so I got the bright idea that I could repurpose this old variable power supply case and build one myself.

    The unit was my dad's and has just been sitting in a shed for ~20 years. Rats had chewed through the wires, and I have no need for it, but didn't want to toss it as my dad was an electrical engineer and used to tinker in our garage with it.

    I found a few other projects online that are similar, but they are for audio only, and I don't know how much more complicated it becomes to add in the 3rd RCA for video. The rough plan:

    • Attach 5 sets of 3 chassis-mount RCA jacks to the back of this case, plus one more set for output (24 jacks total)
    • Replace the main knob on front with a 6 position knob (3 pole??)
    • If I can, I may also add a 1/8" stereo input on the front for smartphones, etc
    • Add different color LED indicators to show which input is selected (I don't plan on relabeling on the front panel)
    • I would really love to at least light up the built-in Volts/Amps gauge, and if there's a way to animate the needle somehow, that would be the icing on the cake. I will also use the on-off switch for the lighting, and I think I'll just have the LED's battery-powered for now.
    So um, where do I start? Disassembly was easy! It seems easy enough to source the RCA jacks, battery terminal and other stuff, but I'm not sure what type of knob would work best, and the best way to switch on the appropriate LED without causing some sort of noise/interference with the audio/video signals.

    Here's one of the examples I located in my brief research so far. I'm not going for anything that high-end, as none of my equipment warrants it.

    Attached Files:

  2. shrtrnd


    Jan 15, 2010
    You'll have to decide on the switch. You may get suggestions from others on this site to follow.
    My input is to be especially careful to use coax or some other high quality shielded wire, or you're going to wind-up
    with crosstalk (unwanted induction of signals and spurious noise from one system to another).
    Check your circuit and figure-out how many selector switch circuits you're going to need. (So you'll know how many switch positions you'll need)
    If you want your system to last, avoid buying a Chinese switch.
    Use good shielding practices and accessories when you put the final product together.
    Last edited: Jun 1, 2016
  3. Gryd3


    Jun 25, 2014
    shrtrnd is spot on.
    The tricky part here will be the actual switch and is the cornerstone of this project.

    As far as actually switching the signals are concerned you don't need anything too *special*.

    Shielding here is important! Without shielding, you will find that your video picks up static... or if the wire inside the enclosure is run parallel to another signal wire, it could pick up cross-talk ... ie, video signal from wire B ends up superimposed on wire A. Coaxial wire is great for preventing this.
    If you keep a decent distance between wires and try not to run them in parallel for too long of a length you may be able to get away with not using coax.
    Looks like the metal box will offer some protection against outside noise anyway.

    A note about the LEDs though... This requires a power source, and these can cause a LOT of noise that will interfere with video and audio signals. If you go this route, you will need a very clean DC power supply or battery for the LEDs, or you may find that omiting coax cable inside the enclosure is impossible and may even be tricky with actually using it...
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