noheadphones Posted March 31, 2009 Share Posted March 31, 2009 Is there any technical difference between a DMX Y split and a bridged pass thru assuming you do not use the DMX out on a fixture. Example: say you were installing some fixtures and you only used the DMX In, but you carried the DMX thru to the next fixture with-in the wall plate. Would this cause a problem? Noheadphones Link to comment Share on other sites More sharing options...
Mr Steve Posted March 31, 2009 Share Posted March 31, 2009 To split a DMX line, you need a DMX splitter/buffer box. I see what you mean in theory, but you'd need to terminate the 'out' of the fixture. However, if you've split in the wall plate, that line isn't really terminated, but going on to another fixture. I expect it would cause problems as that sort of connection is not part of DMX spec, as well as confusing the hell out of anyone else using the system. It's just wrong. Link to comment Share on other sites More sharing options...
Davethsparky Posted March 31, 2009 Share Posted March 31, 2009 yes this most probably will cause you problems. The wires which tee off from the data line to the receiver chip must be kept as short as possible. The signal becomes badly distorted if they are not.In the example you gave anyone could easily put a long cable in from the wall plate to the fixture or daisy chain another fixture from it. Link to comment Share on other sites More sharing options...
noheadphones Posted March 31, 2009 Author Share Posted March 31, 2009 The reason for doing it this way would negate the problem of a unit going down and disrupting the DMX chain (the units have DMX fly leads and so wall plates would have to be installed) Link to comment Share on other sites More sharing options...
Germaine Posted March 31, 2009 Share Posted March 31, 2009 I'm pretty sure the unit would have to go down in a big way for it to disrupt the rest of the DMX line i.e. melt/explode in which case you'd probably want to stop the show/event anyway. It's been a while since I tinkered with this stuff but if I remember correctly almost all moving heads have a chip that converts the +/- signals into a standard digital signal and also provides some electrical isolation. Germaine Link to comment Share on other sites More sharing options...
smalljoshua Posted April 1, 2009 Share Posted April 1, 2009 There is no reason for needing to do this, the DMX in/out in most fixtures are just parallelled anyway. Also, fig 13 on this page shows why this is a problem. Josh Link to comment Share on other sites More sharing options...
smalljoshua Posted April 1, 2009 Share Posted April 1, 2009 Oops, as has been pointed out to me in a PM, I forgot to add the link. This Page P.S. How long after a post can you edit it now? Josh Link to comment Share on other sites More sharing options...
Sound In Gloucestershire Posted April 2, 2009 Share Posted April 2, 2009 ive seen a topic similar to this before it was decided the only feasible way of doing it was to get a DMX Spider and put a cable to each and everyone terminal ill see if I can find the link Link to comment Share on other sites More sharing options...
noheadphones Posted April 2, 2009 Author Share Posted April 2, 2009 Cheers for all your advise. BTW I lost the argument Link to comment Share on other sites More sharing options...
Duncan Wood Posted April 4, 2009 Share Posted April 4, 2009 Is there any technical difference between a DMX Y split and a bridged pass thru assuming you do not use the DMX out on a fixture. Example: say you were installing some fixtures and you only used the DMX In, but you carried the DMX thru to the next fixture with-in the wall plate. Would this cause a problem? Noheadphones It depends on how long the lead to the fixture is. If you're being pedantic it should be less than a 1/10th of the rise time of your DMX signal, practically if it's under 10m it will work provided everything else in the system is good & you only terminate the end of the longest run. However doing it a wall plate means that if you do plug a long cable in it'll stop working in a random fashion. Link to comment Share on other sites More sharing options...
Keeper of the Keys Posted April 5, 2009 Share Posted April 5, 2009 (...) It depends on how long the lead to the fixture is. If you're being pedantic it should be less than a 1/10th of the rise time of your DMX signal, practically if it's under 10m it will work provided everything else in the system is good & you only terminate the end of the longest run. However doing it a wall plate means that if you do plug a long cable in it'll stop working in a random fashion.10m is about 30ft that's three times as long as the problematic length mentioned above in the post mentioned by smalljoshua. Y-splitting DMX lines is not recommended (strongly discouraged/not allowed) for multiple reasons, for one thing it can lead to weird behaviour, for another if you terminate every line the total resistance will be to low which basically amounts to a short and your equipment may be damaged (as mentioned by Nick Mobsby in Practical DMX). Link to comment Share on other sites More sharing options...
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