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DMX Controller, Decoder - gumby question

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by gmoolenaar, Jan 10, 2013.

  1. gmoolenaar

    gmoolenaar New Elf

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    Hi All,
    I am a bit of a gumby in this field and starting off anew.

    I have purchased the ECG-D2-2 from j1sys as the bridge, as I liked the idea of having a larger capacity to run cat5 cabling than a USB dongle offers.

    I then started to review the different options available for the DMX controllers and became confused over the different options avialable at the sites. Sometimes they mention controllers, other times they have called them decoders. Not sure if they is difference. I want to be able to control some 5V led strings and rope lights purchased from Kmart and Target.

    I have checked RayWu:
    http://www.aliexpress.com/store/product/24-channel-dmx-constant-voltage-decoder-DC12-24V-input-3A-24channel-output-LN-DMXTCON-24CH-DC12/701799_554408768.html
    http://www.aliexpress.com/store/product/DMX-512-Module-decoder-DC5V-input-P-N-LN-DMXMODEL-3CH-5V/701799_307297559.html

    http://www.aliexpress.com/store/product/Easy-DMX-LED-controller-dmx-decoder-driver/701799_378111925.html

    The first two are decoders where the last has bother controller/decoder listed.

    The second question I have, is the controllers I looked at have 3 channels with a + input. I assume when connecting multiple strings to the group, you just pair up the + connection into the single connection?

    At this stage, I am not worried about reliability, as I am just going to have a play this year and see where it leads.

    Thanks in advance
     
  2. David_AVD

    David_AVD Bite my shiny metal ass!

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    Yes, for separate strings you common up the +ve wires to the one V+ terminal.
     
  3. OP
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    gmoolenaar

    gmoolenaar New Elf

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    Thanks for the response David:

    1. So can I run a single transistor to the multiple common wires, or would each require a seperate resistor?

    2. I pulled apart a rope light last night, the transformer outputs, 6V-3W and then I measured the output voltage on the controller board across the two wires, the voltage was only 2V(peak). Would this mean I would need to drop the voltage on this line to 2V, or is it because it is sharing a common wire, the voltage is actually 2X2V(4V)? From the reading I have done on:
    http://www.instructables.com/id/LEDs-for-Beginners/step7/Wiring-up-multiple-LEDs-in-series/

    Does this indicate a normal rope light(form Target) with these strands(shared +) would use a combination of series/parrallel hookup? ie: If i was to drop one strand I would supply on 2V but if using both I would need to supply 4V to the common +
     
  4. David_AVD

    David_AVD Bite my shiny metal ass!

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    You've totally lost me there. Maybe a diagram will help me understand the question.

    There's a whole can of worms in that. Was the "transformer" an AC or DC output type? How did you measure?
     
  5. OP
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    gmoolenaar

    gmoolenaar New Elf

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    1. Found out it is recommend to run a resistor on each line, the forum i read also said it could be placed anywhere in the chain.
    2. The output of the transformer was DC. I put the rope lights on solid. The three wires outbound from the controller were marked as +, C1 and C2. I stuck the voltmeter on the + & C1 and then checked the + & C2.

    C1 and C2 would each have 20 LED's connected to each string as the rope light is 4 meters with 40 LED's It is a thin rope as well, so I would guess they are using the 3mm LED's.

    Unless of course the run two strips in parallel instead of series. So this would mean the AMPage would be pretty hi on the 2V supply.

    Correct? Or am I just confusing :)
     
  6. David_AVD

    David_AVD Bite my shiny metal ass!

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    If the power supply was only 6V, they must be running the LEDs in parallel.
     
  7. OP
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    gmoolenaar

    gmoolenaar New Elf

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    Hopefully, my last question before I can start building my display board.

    I plan on connecting up around 400-500 Leds of different colors in a combination of parallel and series. I know each color will need to be on a different channel.

    Assuming:
    • input voltage is 12V
    • an average of 3 V per LED
    • 20 mA per LED
    • max 1 amp per channel
    I can put 5 LED's in a series with a resistor value of around 130R to max out the Voltage and around 100mA

    To reduce my channel usage, I can then connect each string in parrallel to up the number of LED's.

    So do you work out how many strings of the series connected LED's can I connect parrallel? Is it based on just adding the mA so I can connect 10 strings(connected in parrallel) of 5 LED (connected in series) to give 50 LED's per channel?

    thanks in advance...
     
  8. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Take a look at this LED calculator http://led.linear1.org/led.wiz

    just remember that when designing a LED circuit:

    LEDs in series you add the voltage together
    LEDs in parallel you add the current together.
     
  9. David_AVD

    David_AVD Bite my shiny metal ass!

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    For 12V DC, I'd generally suggest no more than 3 LEDs in series. For red LEDs you could get away with 4 or 5 as they have a much lower forward voltage.

    If you set the LED current in each series section to 20mA via a suitable resistor, it's just a matter of multiplying 20mA x how many sections are in parallel to find the total current draw.
     

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