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Assistance with a LED array circuit

Discussion in 'LEDs and Optoelectronics' started by alexanderfoti, Jan 10, 2013.

  1. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Hi all

    This is my first post here, as I was shunned from the "other" electronics forum as they do not allow automotive posts. (makes no sense to me!), so HI :)

    I am looking for some help with a motorbike brake system. I have build some led arrays, 6 leds each in series, then in parallel for a total of 48 led's per board, both boards wired in series.

    A picture says a thousand words so here is the "circuit" Diagram:

    [​IMG]

    Sorry for my crappy drawing, it was getting late and I was frustrated heh.

    The reason for the resistors is that when the headlights are turned on the "tail" line is energised, at a lower current so that the LED arrays illumante dimmer, then when the brake is pressed, the "brake" line is energised, bypassing the resistors and getting brighter. This works when one array is connected, but is back feeding with more than one connected.

    So when I connect the second LED strip (at the bottom of the diag), the LED arrays go out (when on tail mode) when on braking mode everything lights up as it should. Its my thinking that I need some diodes at A and B on the diagram, can anybody confirm if I am on the right track :)
     
  2. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Additionally when connecting the second led strip, when turning on the tail light, the brake lights up as well, I believe due to the lack of the diode, the 13v tail line is energising the brake line (albeit with reduced current because of the resistor)
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Your LED arrays have resistors to limit current, right?
     
  4. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    yes :) The actual array circuits look like this:
    [​IMG]
     
  5. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Im thiking I need a diode on both the 12v tail and brake lines?

    Although I have seen a diagram with a diode between the brake and tail lines, not sure if that would help :(
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    OK, so you want the strip and the brake lights (at low intensity) on as the taillights.

    When the brake is engaged, you want the brake lights to go to full brightness.

    The first thing is to wire up the brake lights as brake lights, and the strip light as a tail light. Get them working as required independent of each other.

    Then take a diode, with the anode connected to the tail-light circuit, and connect it to a resistor and the resistor, in turn connected to the brake light circuit.

    Confirm that the brake alone lights only the brake lights at full intensity.

    Confirm that the tail-lights alone illuminate the strip, and the brake lights at low intensity.

    And finally confirm that with the taillights on, the brake ONLY causes the brake lights to get brighter.
     
  7. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Just to clarify, do you mean connect

    Tail light wire on bike --> Diode ---> Resistor ---> Brake light wire on bike

    Or

    Tail light wire on bike --> Diode ---> Resistor ---> Brake led array positive

    ?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    They should be functionally identical because the brake wire light on the bike should connect directly to the brake LED array positive. (or am I missing something?)
     
  9. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Oh yes you are correct, apologies my brain is a bit mushy, I will give that a go tonight as I am at work at the moment.

    Many thanks.
     
  10. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    When doing the above, should I use one resistor, or 2 0.5w ones as per my original diagram?
     
  11. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Also, I would have to change the restistors in my array to accomodate for the lower voltage?
     
  12. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Update - It didn't work. As soon as I connect the LED strip, the other LED tail light turns off, even with the diode.
     
  13. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Here is a better circuit diagram:

    [​IMG]
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, I asked you to do steps in order.

    Go back to the steps.

    Which ones worked and when did it fail?

    The circuit above looks like you want all three dim as tail-lights, and all three bright as brake lights. Is that what you want?

    Also notice that both of those resistors are in parallel.

    Does the LED strip have its own current limiting resistor?

    What are you using as a power supply to test this (or are you wiring it up on the bike)?
     
  15. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Apologies.

    Wiring the brake light as a brake light - Works
    Wiring the Strip as a tail light - Works

    tail light circuit to Resistor to diode to brake circuit, causes the brake/tail array to turn off and the LED strip to turn on, as before.

    I have noticed that this does work though?

    [​IMG]
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    That circuit will only turn on one of the brake lights at lower intensity as a taillight. (and it will turn the strip light on at even lower brightness with the brakes.)

    You also didn't answer these questions:

    Show me the circuit you have to *just* power the brake lights as brake lights, and the strip light as a taillight.

    I think you're adding way too much more to that circuit.
     
  17. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Sorry, yes the LED strip has its own current limiting resistor, it has a built in one as well.

    I am using a lead acid battery at 12.5 volts, I am also taking the tested circuit out to the bike to test.
     
  18. alexanderfoti

    alexanderfoti

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    Jan 10, 2013
    Here is the circuit just powering the brake as brake and tail as tail:

    [​IMG]
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    OK, take a diode and a resistor and connect them from the 13V Tail line to the 13V brake line.

    That should give you dim brake lights as tail lights.

    See if that works.
     
  20. alexanderfoti

    alexanderfoti

    24
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    Jan 10, 2013
    Right, bit of an update.

    inside the brake light, on the LED arrays, I had 2 resistors connected and 2 cables connected to each other on the positive connection, I ended up not using them but left them connected and forgot about them.

    I pulled them apart and insulated them and it appears to be working correctly as per your original recommendation. I think the reason it didn't work the first time was that the bridging between the lines was happening in 2 places! Whilst I was there, I replaced the resistors in the brake light array with lower resistance to accommodate for the lower voltage caused by the diode. Thanks for your help.
     
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