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LED Circuit?

Discussion in 'Electronic Basics' started by Drew, Mar 14, 2008.

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  1. Drew

    Drew Guest

    I'm trying to apply a tally light system: a Panasonic video switcher
    that sends a signal, and I want a couple of LEDs to turn on 150ft.
    away whenever that signal is on. That's it.

    Whether I'm building it myself or not, I need to understand what the
    switcher does and doesn't handle, so I don't overload any of the
    Panasonic's components - it's a $11,000 device. Here's the information
    I have about its (D-sub15) control output:

    Is it designed to drive LEDs directly, or would you recommend a relay?
    What should also be in there to protect the unit (diodes)?

    The signal has to go through 150 ft. of 26 AWG (7x34) Stranded TC
    wire, rated at 38.5 ohm/Mft.

    I might be able to use an off-the-shelf tally system - Datavideo TB5
    ( Since it's
    designed to connect to their own video switcher, there isn't much info
    available. All I have is the Datavideo switcher diagram, which the TB5
    is designed for:

    Given the right cable, should I be able to connect the TB5 to the
    Panasonic directly and suppose everything will work fine, or not
  2. Andrew Holme

    Andrew Holme Guest

    That diagram shows it driving an LED (with a series current-setting
    resistor) directly.

    You could use a relay or an opto-isolator. I would go for the latter.
    You'll need a local DC power source either way.
    A diode could protect against reverse polarity; you could also include
    transorbs (transient absorbers) and use a screened cable with the screen
    connected to chassis-earth at both ends.
    Looks like it.

    They call it an RS232 cable; but it's not RS232. They might as well call it
    VGA judging by the D-connectors.
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