Signal Selector Using Transistors

Discussion in 'General Electronics Chat' started by ajm113, Oct 29, 2012.

  1. ajm113

    Thread Starter Member

    Feb 19, 2011
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    5
    I was wondering if anyone could give me tips on designing a signal selector. I was thinking on making a 5 in HDMI to 1 HDMI out without using moving parts. This is my first experiment with AV signals and I'm sort of without tools at the moment other wise I would grab a oscilloscope and a HDMI cable and start playing around with some transistors. Now I guest my main question would be is how would I switch something such as AC signals with transistors?

    I ran a simulation of a basic transistor switch I made and it appears it would really mess up the signals, since there isn't good isolation between the two inputs.
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,988
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    HDMI is too much a complex and high frequency signal (three 340MHz differential signals) for a newbie to build an analog switch for. I've had experience in building high frequency circuits and I would not attempt it. Better to start with something simpler. ;)

    If you need an HDMI switch just buy it such as one of these. You are unlikely to be able to build one cheaper.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    If you really want to go for this, look up transmission gates as an analog multiplexer. This will get you started..
     
  4. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    It's not really a 'need', but just for fun to learn. What would you recommend then? RCA? Since it's kinda more old school and maybe more resources on?

    @tshuck: Thanks, I'll look up some tutorials/examples right now. :) If it looks to hard to accomplish this task I'll just find something else to learn.

    EDIT: What if I just use analog switches? Because they would completely isolate the signal from the switch? Correct me if Im wrong. Just thought it would make life a little easier.
     
    Last edited: Oct 29, 2012
  5. crutschow

    Expert

    Mar 14, 2008
    12,988
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    When you are working with 340MHz digital signals, nothing provides perfect isolation or switching. The selection of components and layout is critical. You would need to use transmission line PCB techniques with ground planes. Not for a beginner to try.

    So if you just want to learn, perhaps you could try doing an audio switch or multiplexer using some CMOS devices. Maybe switch some signals to light some LEDs. Here's a list of some standard CMOS parts which includes switches and multiplexers such as the 4051 through 4053 and the 4066 and 4067.
     
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