PaulDF Posted March 23, 2014 Share Posted March 23, 2014 Hi,I am trying to put together a simple box that switches between two DMX dongles, a desktop PC with an enttec open and a laptop PC with an enttec pro dongle. I have had a couple of occasions where the desktop has locked up and stopped outputting DMX so want to firstly be able to see if DMX is outputting and secondly throw a switch to select the other source.As I am trying to keep it relatively simple is there any reason why I cannot use a simple double pole double throw switch to select the relevant RS485 output switching it to the universe, or would I be better switching the signals to TTL and using gates to control them, outputting back to RS485?I have connected the three lots of Pin 1 together (screen)I would also like to be able to see if DMX is available on either of the two inputs, my thoughts are to have a pair of LEDs, one lit on the positive cycle of the pulse and the other on the negative. If the DMX output stops then I'm wanting one of the LEDs to extinguish. I'm thinking that the LEDs will look steady as iirc the signal is 250kb/s.I have attached a circuit below:http://i215.photobucket.com/albums/cc91/Spark-123/Image0002_zpsd8d2e49c.jpgThe chip is rated at 60mA so is plenty for a pair of 20mA LEDs one at a time. The chip sources the 5v supply via an internal 85 ohm resistor and sinks directly to 0v hence the different size resistors I'm thinking on the output. The datasheet for the sn75186b chip is here: http://www.ti.com/lit/ds/symlink/sn65176b.pdf This is what I have built to press, I haven't tried it live yet.http://i215.photobucket.com/albums/cc91/Spark-123/f21a5400-aa52-47f3-bb1a-47276dacfd02_zpsfb108296.jpg http://i215.photobucket.com/albums/cc91/Spark-123/25af0ded-9db6-4e92-b66d-bb0698d3572b_zps2279befc.jpg Any comments appreciated Paul F Link to comment Share on other sites More sharing options...
dbuckley Posted March 23, 2014 Share Posted March 23, 2014 A simple DPDT switch will do. However... the DMX line will glitch when the switch is thrown. How much of an issue this is is up to you. Perhaps the LEDs parcans might flash or do something funny, but the conventionals are most unlikley notice a one frame glitch. If one is doing something dumb like flame projectors without dead mans handle override, then bad things could indeed happen. An "straight" electronic switch will still glitch. To make the feed not glitch you need cleanly stop receiving DMX A, and start outputting DMX B at the start of the frame. This needs microprocessing to decode the incoming stream. Link to comment Share on other sites More sharing options...
PaulDF Posted March 24, 2014 Author Share Posted March 24, 2014 I never thought of that. I only have generics, led pars, smoke machine, hazer, strobe, moving heads attached so hopefully won't be a problem. I haven't had a problem when swopping the 5pin DMX lead between dongles that I noticed but I usually have my head buried in the wires behind computers at the time!ThanksPaul Link to comment Share on other sites More sharing options...
stevefez Posted March 24, 2014 Share Posted March 24, 2014 I've been keeping an eye on this as I'm in the need for a varient of the above. I need to be able to switch between two DMX sources, (a simple DMX wall switch and magicQ PC). The difficulty comes from needing to be able to switch from two different locations. Essentialy, we have house lights on a DMX dimmer, (through an old school Pulsar Demux) and would like to be able to control them them from a wall panel on most occasions, but then switch to controlling them from the MagicQ PC at FOH. Ideally, we would like a DMX selection switch located next to the wall panel, AND next to the LX pc upstairs. A bit like switching on a landing light from both the top of the stairs and the bottom. I'm fairly confident with a soldering iron, but even simple electronics escapes me entirely. Would someone be able to knock up a PaperCad daigram for me? It's a litle cheeky I know, and a similar result could be achieved using a DMX merge, but in our situation, simple is almost certianly better. I even remember this being mentioned before, and it had an indicator LED involved too, however finding the thread has proved difficult...Any help appreciated. Link to comment Share on other sites More sharing options...
smalljoshua Posted March 24, 2014 Share Posted March 24, 2014 Do you really want the ability to let someone override your desk from a position out of your control though? Josh Link to comment Share on other sites More sharing options...
Brian Posted March 24, 2014 Share Posted March 24, 2014 Would someone be able to knock up a PaperCad diagram for me? Like this... If security was a problem, one or both switches could be key operated. Link to comment Share on other sites More sharing options...
sleah Posted March 24, 2014 Share Posted March 24, 2014 Do you really want the ability to let someone override your desk from a position out of your control though? Josh I'd suggest DMX merge may be simpler - if only for the reason above. At least there's no chance anyone could disable desk control from FOH, the worse they could do is put the house lights up! Would DMX merge not also work for the OP? So long as the backup desk was at 0% until required, it would be less likely to 'glitch' although there is still a chance as the main desk goes down that it could spit out unwanted DMX, but nothing in the world could prevent that!With a merge, as soon as the main unit crashed, whack the backup to the required values and yank the plug on the faulty dongle. If the faulty unit had simply 'hung' then it would be a seamless change, provided you disconnected the faulty unit before it spat out something strange.... I have no personal experience of DMX merge so I hope my theory is correct Link to comment Share on other sites More sharing options...
stevefez Posted March 24, 2014 Share Posted March 24, 2014 Do you really want the ability to let someone override your desk from a position out of your control though? JoshTrue, it's a risk, but the ability to be able to switch back to local control from either location probably outweighs the risk... probably. Like this... [snip] If security was a problem, one or both switches could be key operated.Brian you absolute legend. If we ever meet, which is unlikely, I owe you a beer or two. Key operated might be the way forward, I'll have a think about that. I'd suggest DMX merge may be simpler - if only for the reason above. At least there's no chance anyone could disable desk control from FOH, the worse they could do is put the house lights up!That would work, however, we'd like the option of adding some cheap LED bits and bobs to the houselighting down the line. With the correct DMX wallpanel this is easily achieved, [press here for purple wall wash etc...] so in that situation, someone operating the wall panel could impact the room fairly signicantly. However you have me thinking, configuring a DMX merge to preference one input could work. Simply put, if the MagicQ pc is outputting DMX, use that source, if it isn't (switched off) then use the wall panel DMX source. Then all the operator has to do is remember to switch the MagicQ off. Simples. Ah two options, both with their merits. A perfect way to find a solution. Many thanks all! EDIT: Spling Link to comment Share on other sites More sharing options...
PaulDF Posted March 25, 2014 Author Share Posted March 25, 2014 Another great idea, I have looked at a couple on the CPC website and looks like they both have a backup facility which will monitor source 1 and switch to source 2 if source 1 fails, exactly what I am after. I have already ordered some chips and a PSU for the LEDs on the box I have made so will have a bash at that one first, if it doesn't work 100% properly then it is great to have a plan B.Thanks Paul Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.