All LED's fade on and a delay on 4 of the 20 LED's in parallel

Discussion in 'The Projects Forum' started by james555, Dec 20, 2014.

  1. james555

    Thread Starter New Member

    Dec 20, 2014
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    i have a 20 LEDs in parallel 4 of which i need to have a delay of about 4 seconds and all the leds need to fade on. any ideas how i can do this. im reading up on electronics at the moment but i find it difficult to find exactly what im looking for
     
  2. GopherT

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    Nov 23, 2012
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    Could you draw and post a small schematic. Hand drawn and cell-phone picture is fine. Nothing fancy. Draw the LEDs that you have and the note which LEDs need to come on and when.
     
  3. james555

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    Dec 20, 2014
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    __________ _________ __________ ____________ ___________ _________ || || ___ _____ _____ _____
    __________I>_________I> __________I> ___________I> ___________I> _________|| Delay of 2 seconds ||___I> _____I>_____I>_____I>
    3V(2AA) || from here on ||


    sorry best i can do atm.

    very simple i know. i know i could use a 555 for the delay, but i feel as the thats like swatting a fly with a nuke (over kill). there must be a simply way of achieving this. pehaps some sort od capacitor/ transistor combo
     
  4. james555

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    Dec 20, 2014
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  5. james555

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    Dec 20, 2014
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    errrg.. well that did'nt work.

    its a very simple string of 15 leds all in parallel, the last 4 in the string should have a delay of a couple of seconds.

    oh wait... paint! 1sec
     
  6. djsfantasi

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    Apr 11, 2010
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  7. james555

    Thread Starter New Member

    Dec 20, 2014
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    ahh there we go
     
  8. james555

    Thread Starter New Member

    Dec 20, 2014
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    nice!!! thank you for that i will save it :) will mine do or do you want me to moch it up with the new symbols
     
  9. Alec_t

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    Sep 17, 2013
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    What power supply voltage do you have available? It may be more power-efficient to connect LEDs in series.
     
  10. james555

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    Dec 20, 2014
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    3v (2aa)
     
  11. djsfantasi

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    Apr 11, 2010
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    Is this string of LEDs a commercial product? Can you run one additional wire to the point before where you want the delay to display? The commercial strips have built in current limiting resistors. And they often are wired in a combo of serial and parallel wiring. I have a drawing on my laptop and will attach later.
     
  12. james555

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    Dec 20, 2014
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    yeah its a typical commercial product, however iv stripped off the leds for parts (cost effective) so no resistors i suppose. i didn't realize then had them, how would i need to add them. i'v done this before, didn't use resistors and i had no problems? very strange
     
  13. djsfantasi

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    Apr 11, 2010
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    Batteries have an internal resistance, which let's this work occasionally.

    I'll attach my picture later...
     
  14. djsfantasi

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    Apr 11, 2010
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    First, the commercial LED strips are often wired similar (note the caveat) to this:

    strip.png

    That is, they are divided into groups of LEDs connected serially with a current limiting resistor in series. These strips often say, "can be cut anywhere, as long as it is cut between groups of three (or four, or five, etc...) Since you disassembled yours for parts, this information can be useful for making your own strip as described.

    What I have been trying to say is that you can break your strip at a certain point and run one extra wire. Then, you power your first 16 LEDs normally, through an LED fading circuit. The remaining four have the delay circuit before the fade-in.

    leds.jpg
    I'm not going to describe the fade circuit here, but if you use the forums search function for "LED fade", you will get several good references. In Bill Marsdren's blog, there is an excellent reference, LEDs, 555s, PWM, Flashers, and Light Chasers
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    What color of LED's? Or if available the Vf.
    How long is the fade on period?
    Same fade but delayed start for last 4 LED's?
     
  16. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If the LEDs are white or blue then 2 AAs will be inadequate to power them without using a DC-DC boost converter.
    What initiates the fade sequence?
    Is fade out also required?
    In post #1 you say 20 LEDs. In post #5 you say 15. Which is it?
     
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