Noisy LEDS / Long Cabling

Discussion in 'General Electronics Chat' started by mxabeles, Oct 11, 2016.

  1. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Hi there! Built simple circuit (arduino powering 12v .25 mA leds using uln2003 transistor arrays) that works with short wire from led to circuit board. But when I extend wire length I get fair amount of noise - LED never fully off.

    Im using 18awg 2 conductor stranded hookup wiring with rca connectors at microcontroller.

    How can I alleviate noise? I was reading about placing a capacitor at my DC power supply (12v, 5A). Would that help, and if so what kind?

    Also thinking about using shielded wire, but then I would have to ditch rca connectors (would now need three terminals for drain, +12v, and collector pin) correct?

    Thank you for your help ! For show coming up in a week :)
     
  2. crutschow

    Expert

    Mar 14, 2008
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    At what connection are you extending the wire?
     
  3. ci139

    Member

    Jul 11, 2016
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    how - the datasheet shows a limit for simultaneous parallel ON for your LED current assuming it's 250mA not the barely visible 250µA for low voltage leds
    the I/O delay for these transistors is up to 10µs e.g about 25kHz speed limit (with short connections)
    . . .
    if your connection cable is lengthy you may need to protect your LEDs with diodes against reverse voltage spikes there (in 1 random configuration i used 10nF capacitors . . . not sure if they suit everywhere)
     
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  4. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Hi there, Im extending wire from ends of LED to circuit board....
     
  5. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Hi there,
    Hi there,
    I dont fully understand your first paragraph. If it helps to clarify, the LEDS are not fully on when at rest, but dimly lit - the full 250 mA is not being passed through.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    That normally shouldn't cause a problem.
    Try connecting a 0.1μF from the LED lead to common.
     
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  7. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    I may try the diodes. How do I wire them to the LED?
     
  8. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    I should add, there are 4 huge radio towers right outside my windows. Could this be a situational issue???
     
  9. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    So, to be sure that mean a capacitor from negative of led to ground, not collector right?
     
  10. crutschow

    Expert

    Mar 14, 2008
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    You'll have to post a circuit schematic before I can answer that.
     
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  11. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Okay, Ill try to get somethin up. An update: the noise disapears when I lift the cable off the ground. Maybe some power strips or AC cords are bugging it. Either way, its gonna be off the ground for the show...
     
  12. ci139

    Member

    Jul 11, 2016
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    http://www.wayjun.com/Datasheet/Led/1W%20High%20Power%20LED.pdf
    Wayjun Technology Co.,Ltd www.wayjun.com Design and Application
    1. in the ratings to be used within the operating LED current limit function of the resistor. How much resistance will have to refer to the specific product specifications required to calculate the rated current plus that.
    2. LED to be used in parallel mode, each LED channel by adding resistors are required, must not be led directly to multiple parallel.
    3. circuits shall be designed to note: When the LED goes out to prohibit reverse voltage.
    4. circuitry required to design note: the lights, turn off the lights when you prevent the instantaneous voltage. 1W High Power LED
    5. solder direction (electrode direction) to be orthogonal with the direction of PCB.
    6. high temperature will reduce its performance and reliability, please stay away from heat sources.
    i'm not sure i fully decode 3. 4.
    as for 3. the reverse voltage is cancelled by same direction series (a high reverse blocking voltage) diode AND/OR reverse parallel diode
     
  13. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    Hi there, thanks for this.
    I maybe see the confusion...Im not wiring multiple LEDs to each collector pin of the uln2003 (the bold font talks of wiring leds in parallel). I have one 250mA led per collector, that is all. The uln2003 is rated at 500mA per collector so its good.

    As stated, when led cable is lifted off the floor my problem disappears. Im guessing its to close to other strong AC power sources ?
     
  14. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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