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Thread: Invert blanking?

  1. #1

    Default Invert blanking?

    I'm trying to invert the blanking signal but want to do it as easy as possible. Would this work or will it burn the optocoupler?



    It's the schematic yaddatrance made but with some modefications.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  2. #2
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    4N25 optoisolators don't invert signal... What you implemented is a pull up
    resistor (vs a pull down resistor in the original schematic) so in the absence of
    signal from the computer, the line will be 5V (vs GND in the original schematic)

    You'd still have to throw a 74HC04 hex invertor (or an equivalent type such as
    74LS04) in there after the optoisolator...

    When using a 7404 type IC, it is VERY important to ground unused inputs...


  3. #3

    Default

    Yes, when the signal goes to 0 the 4N25 will be disconnected giving a +5 volts on the laser blanking. When the blanking goes on to 1 the 4N25 will connect the blanking line to ground and that should invert the blanking to the laser.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  4. #4
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    Default

    Ah, you're right! Didn't bother looking at the path beyond the pullup/down...

  5. #5

    Default

    I'll give it a try when I come home from work. And then report back if it works as I hope. Could be useful whenever you need a quick and somewhat safe way of invert blanking signals.

    Edit: It works like a sharm but Ihad to lower the value of the resistor to about 5Kohm.
    You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads!

  6. #6

    Default

    yes 10K is too high with high frequency of blanking.
    more when the cable lenght is high.
    the pull up need to charge the parasitic capacitor of the wires
    you can use optoschmitt too because this is fastest.
    like this
    http://wiki.gb.nrao.edu/pub/Projects.../HCPL-2630.pdf
    or with totem output system like inverter behind the optocoupler (more current to drive capacitive load)

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