Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Looking for a opto-isolation schematic for DMX

  1. #1
    Join Date
    Aug 2017
    Posts
    14
    Post Thanks / Like

    Default Looking for a opto-isolation schematic for DMX

    I'm looking to opto-isolate some of my DMX devices, and would rather build my own than buy something off the shelf. I see RPM had a design or two, is there anything specific people are using nowadays? I need to support RDM as well, does that need special consideration?

  2. #2
    Join Date
    Feb 2009
    Location
    Plymouth, MN
    Posts
    9,174
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    I assume you need optoisolation to separate high voltage from low, but there can be other reasons, too. Also, I don't understand how RDM would even factor into it as an opto is generally not programmable. Why don't you explain what's in your head about using which kind of DMX devices and what you intend to do with them. That would give others an idea of the direction your going and you might get more responses to your thread. Right now it's pretty vague.

    BTW, generally speaking, it's usually best to be as complete as you can be when you start a "I'm looking for..." kind of thread. Include diagrams and/or photos of gear you're trying to work with, proposed layouts, etc.

    http://digwdf.com/store/
    The DIGWDF Store is closed for all sales. Thanks to everyone who supported us through the years!
    User guides, documentation and other files are still free and available for downloading.

  3. #3
    Join Date
    Aug 2017
    Posts
    14
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    The reason I brought up RDM is that, for some reason, I thought most isolation circuits only work "one way", which is fine for regular DMX but NOT for RDM (bidirectional). Basically, I would like isolation to protect the DMX gear from ground loops or other abnormalities on the DMX line. Here's a good primer: https://auschristmaslighting.com/wiki/DMX-Isolation. According to this link:

    https://www.controlbooth.com/threads...fections.4445/
    "In RDM's early stages of development, they discussed using pins 4 and 5 for return data, but in the final spec, the retun data comes down pins 1 and 2. It is sent on the same wire pair as the normal DMX stream, in between packet breaks. No new wiring is needed, just RDM compliant opto splitters, (that can pass the return data)"

    I'm looking to install a significant amount of DMX fixtures on my building, but I'm afraid I may start blowing out my DMX gear (Let's say an Enttec USB DMX dongle) without proper isolation. Thanks!

  4. #4
    Join Date
    Feb 2009
    Location
    Plymouth, MN
    Posts
    9,174
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    I doubt you'll find many "DIY" circuitry projects here for such use. If you're thinking of theatrical projects and the like, there is plenty of commercial, heavy-duty gear available for that. If you're looking for DIY lighting projects, I don't believe there has been much need expressed for RDM since the protocols that Christmas light enthusiasts generally use are rather asynchronous and to keep the cost down, Ethernet has really come on strong in place of using a serial DMX control structure. Sporadic's excellent DMX firmware for the ESP wireless chip/module is proof in the pudding there and the nature of the Ethernet connection provides some basis of monitoring if it's necessary. On top of that, a wireless connection protocol is, more-or-less, the penultimate "isolation" circuit. (Sporadic's firmware does allow OTA "over-the-air" updating, by the way...)

    I may be way off base here, but a light show is generally a fast-paced activity and there isn't a lot of monitoring of the lighting fixtures going on and unless there's an imminent possibility of a lightning strike, I don't think DIY'ers worry too much about any damage to the gear. The signal voltages and current through the DMX wires are so low it's a non-issue, and there's almost always some sort of optocoupler in the fixture itself at the end of the line before any high power gets involved.

    This probably doesn't answer your question, but unless the application is a mission-critical implementation, most DIY projects seem to be results-oriented and not necessarily process-oriented. As such, a lot of shortcuts may be taken -- again, primarily to minimize cost. Many of us are also constantly on our guard so we don't "over-engineer" a project and make it much more complicated than it really needs to be; somewhat like wrapping a couple layers of electrical tape over a wire connection that's already well encased in shrink tube with the thought that the added tape will somehow make the electrons flow faster. To that end, one might determine just how necessary RDM is in your implementation. If it's a must-have feature then perhaps you might look toward the commercially manufactured products instead.

    http://digwdf.com/store/
    The DIGWDF Store is closed for all sales. Thanks to everyone who supported us through the years!
    User guides, documentation and other files are still free and available for downloading.

  5. #5
    Join Date
    Aug 2017
    Posts
    14
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    I realize RDM is not popular with the DIY crowd, but I saw some schematics floating around and wanted to see if anyone was using them successfully. Even without monitoring, the ability to remotely assign DMX channels is a pretty handy feature with RDM. As they say, it's faster than a ladder! Just to clarify, I'm not looking for isolation on the network side (Ethernet is inherently isolated), but on the DMX side where it really matters. Wireless isolation doesn't fix the problem that DMX isolation is trying to solve.

  6. #6
    Join Date
    Nov 2010
    Posts
    34
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    So attached is the schematic of a DMX/RDM sniffer I created last year. Its not a full isolated RS-485 physical interface but add 2 more opto-couplers and your well on your way.

    Note that the opto-couple is also inverting the signal received to make it comparable with a UART interface.

    The opto-coupler and the 5V isolated supply chip are next to each other on the PCB.
    Attached Files Attached Files

  7. #7
    Join Date
    Aug 2017
    Posts
    14
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    Very interesting! How hard would it be to make it fully isolated? It's also bi-directional?

  8. #8
    Join Date
    Nov 2010
    Posts
    34
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    2 more opto-couplers in the reverse direction driving the RS-485 driver, one for direction change TX/RX and one for serial transmit.

    The main problem using opto-couplers is the space they take up on the PCB and the price of them.

  9. #9
    Join Date
    Nov 2010
    Posts
    34
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    This is an example of what you need, note I have not tested this and cannot verify it but it looks ok:
    https://electronics.stackexchange.co...opto-isolators

  10. #10
    Join Date
    Nov 2010
    Posts
    34
    Post Thanks / Like

    Default Re: Looking for a opto-isolation schematic for DMX

    Here is another one you'll like https://github.com/AlexDWong/DMX-Card in here you can find schematic and PCB layout.

    Again I have not used it and cannot tell how got it is.

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •