I would like to make an AV switchbox

Discussion in 'The Projects Forum' started by Pixel_Outlaw, Jun 30, 2010.

  1. Pixel_Outlaw

    Thread Starter New Member

    Jun 30, 2010
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    Hello,

    I am mostly a hobbyist game programmer but slowly electronics are catching my interest. I have about 9 game consoles hooked up to my television (spanning the mighty Atari 2600 to the Wii) and currently I am forced to use two daisy chained RCA selector boxes. Ideally I would like to design and wire my very own many port RCA selector box. I've very new to electronics hardware. I do know that each game console uses 3 RCA plugs (Red = Right Audio, White = Left Audio, and Yellow = Composite Video). I also know that an RCA connection has both a positive lead and negative lead.

    * I have purchased 60 surface mount RCA connectors for the ports (bulk via eBay).
    You can see one of the 60 here. (I'll just pretend the green is yellow. Hey Italian colors are classy!)
    [​IMG]

    * I was wondering how to use rotary switches to select between the connections. My knee jerk reaction is to use 3 "1 pole 12" position rotary switches, one for video, one for right audio and one for left audio. Each position would point to one device. For a total of 12 connectable devices.

    Any thoughts here? Basically I want to make a system selector for 12 RCA (Red, White, Yellow) devices. I don't know how to connect it all however.
     
    Last edited: Jun 30, 2010
  2. Pixel_Outlaw

    Thread Starter New Member

    Jun 30, 2010
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    I could not find an "Edit" button so please excuse the bump, would something like this work? Again I don't have much experance... This would be one of my 3 switches and would only control one part of the 3 port cluster of AV jacks for every device...
    [​IMG]
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Good on you mate for trying!

    Yes your idea is sound, there are expensive commercial boxes which work the same way.

    Comments:

    RCA connectors don't have positive and negative, they have signal (hot or live) = the tip and earth = the outer .

    You can obtain 12 way switches with three poles so do the job with one switch. The arrangement in your diagram corresponds to a single pole.

    You need break before make switches to avoid connecting the outputs of two devices together, this is the most common type.

    This kind of passive (not powered) switching is prone to crosstalk and general interference between switched signals, especially at higher frequencies ie video. If this becomes a problem there are electronic switching schemes to over come this - at a price.
     
    Last edited: Jul 1, 2010
  4. retched

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    I am in agreement with studiot, As I would go with a 3 pole 12 position rotary break-before-make.

    Just one thing about crosstalk. Are you going to leave all of them powered at the same time?

    For instance, do you pause one game on one system and switch to another system to continue another game? If so, the video signals will be continually transmitting and may cause ghosting or interference. i.e. You will see part of one game in the background of another game.

    If you usually shut down before playing the next console, this won't be a problem.

    You also may be able to find a rotary switch that is made for video signals that uses shielding to help prevent or lessen the chance of crosstalk.
     
  5. Pixel_Outlaw

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    Jun 30, 2010
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    Thank you both.

    I'm confused about how the 3 pole 12 position switch works. How can I only use one switch for my 12 devices (each having 3 seperate signals)? Are there enough solder points?

    I do not usually play more than one console at a time so I don't think ghosting would be a problem. However, if I accidentally leave a console on is this dangerous to the others?
     
  6. retched

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    The 3 poles switch 3 points with each "click" so a 3 pole 12 position would have 36 pins.

    So a search on digikey.com to look at them. When you see it, it will make sense.

    here:
    http://www.electro-nc.com/rotaryus/m5.pdf

    and:
    [​IMG]
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Your RCA jacks are not SMT, they are thru-hole devices.

    You could download the freeware version of Cadsoft Eagle, and create a library model for your jacks, or perhaps there is an existing model.

    http://www.cadsoftusa.com

    There is a decent Eagle tutorial here:
    http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=108

    The freeware version has a 3"x4" (approx) limit to board size. It'll probably be too much of a challenge to place all of those connectors on a single board.

    The switch they are talking about is like three 12-pole rotary switches in one stack. There are three separate "decks" to the switch.

    Your big problem is likely to be ghosting on the video due to impedance mismatches. TV composite video should have 75 Ohms impedance in the transmission line.
     
  8. Pixel_Outlaw

    Thread Starter New Member

    Jun 30, 2010
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    Hurray! My 60 RCA clusters arrived today.

    SgTWookie, thank you for the advice but I already have AutoCAD 2004 for most of my CAD needs, unless you were trying to tell me something else. Are you saying that the switch and "mismatch" is going to still cause picture problems even with other devices turned off?

    Also, thanks for the correction on my understanding of that switch. I hope it is not too costly or I will have to reconsider.

    It is going to be great actually making something rather than relying on prepackage store bought mystery boxes. I can see why Radio Shack has such a crappy selection, nobody wants to just dig in and invent as much as they used to.
     
  9. retched

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    If your other units are off, you will be fine.

    Autocad is fine if you want to create all of the components and such. But the program SgtWookie was talking about, has many components in its library, along with tools required to make a pcboard and check your "wiring" to make sure things are buttoned up properly. Autocad will just draw it.

    With eagle you can print the finished board on a laser printer then fabricate you very own PCB and etch the copper at home. Eagle (And other schematic and PCB layout programs) will keep the sizes proper and can even route the traces automatically.
     
  10. Dx3

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    Jun 19, 2010
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    If I may be so bold, the 3 decks of 12 add up to 36 solder points and add the 3 wipers makes 39.

    I have seen a switching device that used chips to do the actual switching. The "switch" that you move with a knob only sent DC to command which switch should be "on". Very sanitary (keeps the signals clean), but way more complicated. I say, Try the easy way first, and good luck to you.
     
  11. retched

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    Yes, you may be so bold. ;)
     
  12. Pixel_Outlaw

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    Jun 30, 2010
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    I cannot for the life of me find this 12 position 3 pole switch for a low price. I hesitate to ask, but what are my options for under 10 dollars? I'm on a college budget :) . Most places I've been want 50 to 150 dollars for a single switch! The usual eBay is turning up nothing but 3 pole, 4 positions or 1 pole, 12 positions.
     
  13. retched

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  14. SgtWookie

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    Did the seller provide a manufacturer and part number for your triple RCA jacks? That would make creation of a library model a good bit easier than trying to make the measurements yourself.

    Post the info if you have it, or even the datasheet for them.

    AutoCad is a superb tool for mechanical drawing, but like has already been said, it would be a pain to use for drawing schematics and from there creating a viable PCB. Unless, of course, you simply wish to run wires for the audio and coax for the video inside a metal box. However, you really need to mount those jacks on something.
     
  15. Pixel_Outlaw

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    Jun 30, 2010
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    Sorry, I have no information about these particular jacks. I finally saved up the little extra fun money to purchase the 15 dollar switch I need. I guess before I purchase that I would like to ask about my other switch options. Anyone else have ideas? Or is the rotary switch still best? I guess I should have asked for all possible good ideas before giving the impression that I was locked into one type of switch.
     
  16. retched

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    That really is the best for the money.

    It will switch all three lines at once (Left Audio, Right Audio, and Composite Video) and give you the 12 positions for 12 different devices.

    Now you just need a cool-looking knob to attach to it.. Maybe something LED lit? ;)

    Have fun with it.
     
  17. Pixel_Outlaw

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    Jun 30, 2010
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    Well, I had planned to make a classy 1970's looking box. Simulated wood housing and black/chrome knob! I'm a sucker for vintage looking electronics, they are so afraid of certain colors these days. Everything now is sadly black or white with glossy finish.
     
  18. retched

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    I wood (hahaha) go the 70s route. You could also look into steampunk designs if you like wood and metal together.
     
  19. studiot

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    Post a photo when you've done.
     
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