Need assistance with a RCA switcher... Please!

Discussion in 'The Projects Forum' started by octavio, May 31, 2013.

  1. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    Hi, im new to this forum and to electronics overall. Firsts of all pardon my english (its not my native language) and my ignorance.

    So, I have a collection of consoles in my room, its about 9 consoles and most of them uses RCA cables to send signals. Sadly my tv only have 3 RCA inputs and that is annoying when switching consoles. Thats when i decided to buy a RCA switcher, but finding one with enough inputs is challenging and the few that i have met with are very expensive. I thought "why buying one instead of making one?" and i choose to make one. I had two theories about switching videos, the first one its the most obvious: switching all signals at the same time while all grounds are connected. The other one consist on connecting all signals (inputs and outputs) of the same kind together, so I would have a 3 wires and then separting the ground from both inputs and outputs and switch them.[​IMG] (note: black means ground) (srry for paint and horrible schematic)
    But it some how failed, when switching the image stayed in the tv and started glitching out as if it the connection was foulty and made a scary sound before it disappear. Fortunately, no harm was done to the tv nor to the console.

    Of course im siding with the former, which its way easier to understand and it worked like a charm. After searching for the parts on the internet, i came across this 4 pole 23 position rotary switch, which its enough for my projects, i would use 3 poles for signals and 1 for a led indicator. But there is a problem, its a make-before-break switch. I dont think its a big deal since i wont have more than 1 or 2 consoles on at the same time. But then the question rises, "what if they are next to each other and i decide to switch between them?" i dont think it would make any kind of harm to the tv, but I rather be cautious, will it be harmfull?

    http://www.ebay.com/itm/330794252504?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
    http://www.ebay.com/itm/120448579259?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
    http://www.ebay.com/itm/221141894034?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Sharing a common ground for all and switching only the signal is the right strategy. You are right to worry about make-before-break, since this will put two signals in contact with each other. Can you get away with this? Probably. Is it right? No. Maybe someone here can tell us if it's OK to connect two line-level signals.

    Personally, I'd keep looking a bit more. You really only need 3 positions, right? I think even a 3-position toggle switch would work.

    How does the LED fit in?
     
  3. RayInMS

    Member

    Dec 12, 2012
    89
    1
    I don't know about the video signal, but connecting R/L stereo signals into a mono signal is quite common at line level. I don't see a major difference between that and a Ra/Rb connection - especially if it's quick. I think the OP may regret the way he wants to do this after trying to cleanly strip RCA cables without breaking that damned skinny ground filiment, er, wire.

    I'd go with a simple patch bay. Cheap, no cable stripping, avoids the make/break issue, and much easier.
     
  4. RayInMS

    Member

    Dec 12, 2012
    89
    1
    Here's a diagram of a simple patch bay, Octavio.

    All you have to do is solder connections between Input 1 and Output 1, Input 2 and Output 2, etc. Then all you need to do is run the RCA cable from the desired output to your TV RCA Input (shown on right).
     
  5. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    Thanks for the responses,

    Wayne, the leds goes in a column and indicates the position of the rotary switch, an example is something like this. [​IMG]
    In this case its a 12 position switch, engraving the numbers in around the dial would be very hard and may look ugly, so using LEDs to mark the position of the dial is much better, i dont plan to use numbers as lables, i plan on using names (NES, SNES, etc) Keep in mind that in reality its going to be 23 in and 1 out.

    Ray, sorry i dont seem to understand how a simple patch bay works.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Got it. That means you do need that pole.

    So you need 4 poles - audio L and R, video, and LED power - and maybe 12 positions for your various devices?

    I guess one thing I should mention is that you could just use an A/V receiver. You can buy them used on ebay for the price of dirt if they can't do HDMI. (I've been a seller and didn't get much :( ). This would handle all your switching nicely, do a bunch of other stuff, and would include a remote. Few would handle 12 inputs.
     
  7. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    audio switching can be done with a 4066-you can expand it to as many ips as you want-you may also add an ampifier also to buffer the signal on the output.
    will be slightly different regarding cvbs signals as the switching needs good isolation at source and a buffer amplifier may also be needed.
    With the video side of it synchronisation on switching sources may be a problem but if you can put up with the short amount of time it will take for the set to settle down synch wise after you switch inputs it will be fine
     
  8. RayInMS

    Member

    Dec 12, 2012
    89
    1
    A patch bay is just a series of female connections that requires manual operation (i.e., switching a set of plugs) to switch inputs. So, no switch required. I would like to add that using an LED to indicate your inputs does throw a kink in things a bit. What's your power source? How will you isolate the LED part of your switch from the A/V signals?

    I was going to do something like this for a set of audio filters, but decided against it because of the complexity and time involved.

    A patch bay is nothing more than a series of female-to-female bulkhead connectors. It's main function (regardless of application) is organization and simplicity. Here is a link you may want to check out.

    http://news.cnet.com/8301-17938_105-57568957-1/how-to-make-a-video-game-console-patch-bay/

    Use some Google-foo and see what others have built.
     
  9. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    Wayne, thanks for the suggestion but i want to learn with this project. If it fails i may try one of those.

    Sheldon, thanks for the feedback but i think your suggestion its for a more experienced person, right now, i know very little electronics and im trying to learn more.

    Ray, Right now i dont know which adapter to use, i have alot laying around, i think im gonna use a 7.5v 1000ma, i havent thought about it yet but i dont think its that hard.

    I've found a better rotary switch, its about double its price but i beleive it have a better quality http://www.ebay.com/itm/Centralab-CRL-PA-4007-Rotary-Switch-4-Poles-23-Positions-Non-Shorting-Phenolic-/221153859118?pt=LH_DefaultDomain_0&hash=item337dcc162e what do you think?

    I also tought about using a second column of LEDs that indicate activity, but im afraid i dont know how to make this happen. Can it be possible?
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Certainly possible, but not simple to do non-invasively. I'd recommend saving it for gen 2. Maybe leave room for the LEDs and a small PCB but get gen 1 working before moving on to the next level.
     
  11. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    Good idead, i already have some ideas for gen 2, i was thinking about controlling it with my tv remote. It have 4 useless buttons which are color coded (red blue yellow and green) maybe i can use it to make 3 digit color codes (64 possible combinations), change the rotary switch for a rotory encoder and control it with some kind of microcontroller. I've got a lot of learning to do...
     
  12. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    if you can use a soldering iron and can read a schematic im sure a simple 1 transistor buffer for audio and a 2 transistor cvbs amp wont be all that hard....im sure as well that any extras such as adding leds wont be too hard either and the good thing with this site is you can get step by step help to get it done
     
  13. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    I guess you are right, if its simple enough to undertand and to wire ill give it a try. Ill need to investigate a little further.

    I think im gonna go with the make-before-break switch, since ive read that it makes no damage to the tv.
     
  14. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    one other thing to be aware of as your tv uses a switch mode supply you need to ensure that you dont make any connections other than at the sets input sockets provided and do be aware the chassis of your set is at half mains potential and is very much live at all times with respect to earth.....so no tapping any signals anywhere internally on your set or you will release the magic smoke with a loud bang and a dead set.....if you have any test gear use an isolation tx to connect your set to the mains supply before any connections are made (scope wise etc) meters will be ok as long as you are sensible
     
  15. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    Sorry, i dont seem to understand :(
     
  16. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    as long as the leads you make are connected to the inputs on your tv that are provided by the sets manufacturer and the equipment you connect to your leads are powered by their own transformer type power supply you will be ok-its only if you open the set up and start making connections elsewhere in your set you will have problems.
    your tv uses a type of power supply which is not mains isolated so any incorrect connections may mean your leads and any equipment connected may well be at half mains potential with respect to mains earth if not properly designed .....
     
  17. octavio

    Thread Starter New Member

    May 31, 2013
    7
    0
    Yeah, i would be aware of that when building it. Never thought it that way though.
     
Loading...