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Best way to switch video sources — Parallax Forums

Best way to switch video sources

Jim FouchJim Fouch Posts: 395
edited 2005-11-17 16:03 in General Discussion
Not sure if this belongs here or in a different forum, but I'll ask and see what happens.

I'm working on a video project where I want to switch between 4-5 different video signals using an SX.

I'm thinking of using just regular old relays, but am wondering if it would cause·noise. This will be on a motorcycle so there will be some vibration. Maybe I should use SSRs instead???

From an SX stand point, my guess would be to have a common ground and just switch all sources OFF then switch on the Single one I want to be the current source.

Is there a minimum amount of time I should wait between turning off all sources and turning on the one I want?

The switching will be done by a user, it's not a continous process.

Thanks,

Jim Fouch

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-11-16 19:22
    Jim,

    ·· An SSR will not switch a video signal, and a mechanical Relay will, but may introduce some noise into the signal.· There are many small chips (ICs) that the BASIC Stamp can talk to which are made just for this purpose and require very few extra parts.· There was such a circuit listed in a recent Nuts & Volts.· It also showed how to switch Audio as well.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • BeanBean Posts: 8,129
    edited 2005-11-16 19:25
    At my work we use a vishay DG535 it will switch between 16 different sources using just 4 pins. For 8 sources you would only need 3 pins.
    http://www.vishay.com/docs/70070/70070.pdf

    If I remember these are kinda hard to get. If you need one send me a PM (Jim ONLY).

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "SX-Video·Module" Now available from Parallax for only $28.95

    http://www.parallax.com/detail.asp?product_id=30012

    "SX-Video OSD module" Now available from Parallax for only·$49.95
    http://www.parallax.com/detail.asp?product_id=30015

    Product web site: www.sxvm.com

    Those that would give up freedom for security will have neither.


    Post Edited (Bean (Hitt Consulting)) : 11/16/2005 7:31:29 PM GMT
  • MayfieldMayfield Posts: 5
    edited 2005-11-17 16:03
    Bean is correct about the DG535, I've used these with nice results.
    If you want to use Relays and need high isolation between sources, you might want to take a look at the PDF file that Bean referenced, on page 5-10, Fig-12.

    http://www.vishay.com/docs/70070/70070.pdf

    This shows the switching arraignment of the "T" Switch, and can be implemented using Relays or·CMOS switches.
    The "T" Switch provides a high degree of isolation.
    That third switch to ground, helps·short out any crosstalk between the input and output switches when they are open.
    Even though Video might be only a few Megahertz, the harmonics can be very high and love to jump across open contacts.
    It's tempting to use all three contacts in a single relay, but, it is probably best to use a second Relay for either the input or output switch.
    Also... use Break before Make if possible.
    Watch any Circuit-Board Layout, too.

    Tom M.
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