need to build a opto-isolator for my dmx interface

Discussion in 'General Electronics Chat' started by Jacquesl, Mar 31, 2010.

  1. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    Hi, I need to build a opto-isolator for my DMX interface, it's a homemade oksidizer USB to DMX512, and it doesn't have a opto-isolator in it, and I have a problem, my dmx adapter freezes up because one of my DMX lasers makes a spike in the chain on Pin1(ground) and Pin3(positive), and therefor it makes my dmx adapter freeze up heavy.....:mad:
    I do have a terminator.;)
    So have anyone done this before..?

    EDIT: So I'll need to have a opto-isolator on DMX out line, it's like a DMX splitter "witch have a build in opto-isolator in", but buying a splitter is extremely expensive and unnecessary
     
    Last edited: Mar 31, 2010
  2. Norfindel

    Active Member

    Mar 6, 2008
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    I don't know what's a DMX, but i understand that the problem seems to be the USB power, so what about using a powered usb HUB and connect it there? Or make a sort of usb bridge that powers the device from an external supply?
     
  3. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    Ok, DMX is a protocol that is used to control DMX DJ Lighting, and my adapter is a USB to DMX convertor/adapter, so...hehe
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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  6. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    Do you know of a replacement I can use for SN75176, I can't find it in any shop, ZA :cool:
     
  7. bertus

    Administrator

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  8. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    thx man, I just need a design with parts that can be obtained easier, lol
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The availability of components strongly depends on where you are located.
    Where are you located? please update the location in the profile.

    Bertus
     
  10. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    South Africa
    :cool:
     
  11. JDT

    Well-Known Member

    Feb 12, 2009
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    Do you want a transmitter or a receiver circuit?

    Here is a receiver circuit that I have designed and used. Uses the 75176 but there are quite a few alternative I.Cs that you can use.
    http://uk.farnell.com/national-semiconductor/ds75176bn/bus-transceiver-75176-dip8/dp/9487190

    Try SP485E:-

    http://uk.farnell.com/exar/sp485ecp-l/transceiver-rs-485-dip8-5v-485/dp/9387161

    I get the isolated +5V supply by using a very small DC-DC converter:-

    http://uk.farnell.com/xp-power/ie0505s/converter-dc-dc-1w-5v/dp/8727694

    The circuit diagram shows input to a PIC microcontroller.
     
  12. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    The one I need is a sender, from dmx dongle to dmx lights, I see the circuit diagram is for a receiver, I'll check it out, Have to go now
     
  13. JDT

    Well-Known Member

    Feb 12, 2009
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    Basically the sender is much the same. Same driver and opto-coupler and DC-DC converter - signal goes the other way.

    Note that the sender (transmitter) has a terminating resistor across the pair, normally 120R. At the receiver end there are normally two connectors (always 5-pin XLR on "quality" equipment) so that the line can be looped to other receivers or a terminating plug fitted.

    In my opinion, isolation is essential. If you are building a USB to DMX you need to protect your computer!
     
  14. Jacquesl

    Thread Starter Member

    Dec 9, 2006
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    interesting, I've got a terminator that is 100 Ohms, is that also ok? Currently to avoid that spike coming in my adapter, I'm running my dmx dongle without a pin1 attached, "Ground" and it work without any problems, is that safe?
     
  15. JDT

    Well-Known Member

    Feb 12, 2009
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    The value of the terminating resistor is not that critical. Open circuit causes reflections that can corrupt the signal.

    Running without ground connected risks damaging the receiver/driver chip. It is not isolated because there are on-chip diodes that prevent the signal from going past the supply rail voltages. In fact, many circuits have zener diodes between the signal wires and pin1 to protect the chip.
     
  16. SpielbergRules

    New Member

    Mar 27, 2011
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