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DMX testers

Discussion in 'Lighting and Electrics' started by cruiser, Oct 11, 2003.

  1. cruiser

    cruiser Active Member

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    I was just wondering if you've made your own dmx tester in the back of a 5pin canon, how you did it?

    I made one recently, by connecting two 1/2watt 270ohm resistors onto pin 2, so it also works as a terminator, then briding one resistor straight from pin 2 into pin 3 which acts as the terminator, then for the tester i connected a 5mm bi-coloured led onto the end of the other resistor on pin 2 and then ran the other lead of the led into pin 3.

    I was told, if you take all the channels out on the desk and put the tester on the end of your link it will flash one collour, then put some or all of your channels up and it will flash the other colour. but mine only flashed one colour either way... did i do something wrong? :!: :?: :roll:
     
  2. DMXtools

    DMXtools Active Member

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    Quite often, bi-colour LEDs are assymetrical - the green requires a slightly higher forward voltage and/or current than the red. Because the differential voltage between pins 2 and 3 is fairly low, I'd suggest eliminating the resistor you've connected directly between those pins and reducing the value of the series resistor to about 82 ohms. While this isn't perfect termination for DMX-512, it's usually close enough and won't damage anything. I would recommend reverting to 120 ohm termination when you're done testing.

    John
     
  3. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hi Cruiser..not sure if you made this tester based on this website or not:

    http://www.emanator.demon.co.uk/bigclive/dmxtest.htm

    He explains the building process--tho I have not tested his design... I believe he uses 1/4 watt resistors...not sure how much that matters.. The voltage accross a DMX pins 2 & 3 is about +5 or -5 volts...what is the voltage requirement of your bi-color LED, and have you check to ensure both colors are working?

    Now--another possible reason is your tester works fine and is telling you there is a DMX problem with your console. When a line is "stuck high" it will remain constantly on and only one color. A DMX testor I have will do that if there is aproblem with the console or isosplitter DMX signal. Check out Doug Fleenor Designs...he has a ton of articles on DMX and so forth.

    http://www.dfd.com/tstr.html


    wolf
     
  4. cruiser

    cruiser Active Member

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    Yeah... I used plans similar to that, The DMX line i used it on was in a pretty old dodgey theatre, I will try it again on a proper dmx signal.

    Yes, the bi-coloured led was working before i put it in, and did flash both colours. Its not a big issue, i mean i can work around it its just that it is slightly frustrating!
     
  5. cruiser

    cruiser Active Member

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    Alright...Let me firstly say, sorry for dragging up an old post, even moreso because it was originally by me!

    I have created my own DMX tester, and it doubles as a mic cable checker!

    What you need:

    Two different coloured LED's (try for 8-30mcd) and in the 2.2v area.
    Two 560ohm 1/4watt metal film resistors
    A 5pin male canon jack

    What you do:

    1. Solder 1 resistor onto pin 2 and one onto pin 3.
    2. Solder the anode (long leg) of one LED to the resistor on pin 2 and the anode of the other resistor to on pin 3.
    3. twist the cathode (short leg) of both LED's together and solder it to pin 1.
    4. Stick the LED's up through the hole in the top of the canon jack, and fill the base with silicone, or super glue around the edges, as it does not have the stopper inside it when u push and pull it out of the female connector your plug will tend to slide right in...

    Now, it should flash one colour when you have lights on, and the other colour when there are no lights on.
    If you then go and get or make a 5 to 3pin converter, and have a dodgey mic or something, switch on phantom power and stick the tester in the end of the mic lead, if both colours don't light it means your lead is screwd if pin 2 lights it means the -ve is stuffed vice versa if neighter light then the lead is completely dead =)

    Sound pretty simple in theory... if ya want a block diagram or anythin else email me [email protected]

    Good luck!
     

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