555 fading LEDS

Discussion in 'General Electronics Chat' started by adamclark, Nov 13, 2013.

  1. adamclark

    Thread Starter Member

    Oct 4, 2013
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    hello again,, Im working on a Christmas light project with my children. We are building the star for our tree with blue LEDs and I want to make them oscillate, flash and fade. Ive worked with the 555 timer a few times and I know I can make them either oscillate or flash all at once with them, but I want to be able to make them do all of them either on a cycle or be able to choose which one they do. I think a 555 can do this but I cant find a schematic for it anywhere. I appreciate any help you can offer.. thanks
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Have a look at the 4017 if you want them to flash in sequence.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You can put a capacitor in parallel with the led to slow the pulse down, like this circuit,

    or use a counter chip to give a moving chase effect, again put caps across the leds with a series diode to block the discharge by the chip.

    chaser circuit
     
  4. adamclark

    Thread Starter Member

    Oct 4, 2013
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    thanks for the ideas,, will definitely check out the 4017.. what do you think would cause a shimmer effect,, kinda like real stars flicker some.. I just want it to do something other than just flash..
     
  5. bertus

    Administrator

    Apr 5, 2008
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  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You could also use two 555 timers with slightly off frequencies (100 Hz and 101 Hz) then run both through and AND gate to get a beat-frequency oscillation and duty cycle would vary the apparent intensity. Temperature effects may cause the frequency to shift a little over time and, therefore, a lot of shift to the visible beat frequency. It could be fun though. You might need a pass transistor if you are driving more than one LED from the AND gate.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    I have several different ways to fade LEDs with 555s in my article...

    LEDs, 555s, Flashers, and Light Chasers

    If you define what you would like a bit tighter I could probably help draw something specific.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Or use a flickering candle LED to drive the blue LED's. For more of a shimmer than flicker, partially filter the candles PWM signal.
    Do the LED shimmer together, or in smaller groups. How many LED's?
     
  9. adamclark

    Thread Starter Member

    Oct 4, 2013
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    Thank you Bill_Mardsen.. I was really just waiting for you to chime in.. I would like to use 555 timers as the only ic I use, I would like for the LEDs to flash, oscillate, fade, and flicker(but I think a high oscillation rate would cause that effect). And I would like to cycle through each effect with a single button or have them cycle through all of them automatically...
     
  10. GopherT

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    Nov 23, 2012
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    That is a tall order for a 555-only circuit.
     
  11. adamclark

    Thread Starter Member

    Oct 4, 2013
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    I know,, Im open to other ic's as well. but im still learning so I wanted to keep it as simple as possible.. What I don't want due to time constraints and skill levels are the use of microcontrollers.. if I could achieve what I want from a small circuit with a few different ic's then its all good.. the main reason for the 555 only circuit is because ive used them before and am kinda familiar with them,, and the fact that I have over 20 of them just hanging out in my box...
     
  12. Wendy

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    Mar 24, 2008
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    Have you looked at From Four, Twenty? I was basically thinking Christmas Tree lights when I envisioned it.

    It just occurred to me you could use the fader circuits along with this schematic. Not sure how it would look, but it could be interesting.
     
    Last edited: Nov 14, 2013
  13. ScottWang

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    Aug 23, 2012
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    Twinkle, twinkle, little star, How I wonder what you are.

    Whatever you call it twinkle star, breathing LED, slow bright and dark LED, they are almost the same idea.

    You can changing the frequency of NE555 to make the LED lighting time keeping longer, or adjust the values of R2,R3,C3 to changing the time of going bright and the time of going dark.

    [​IMG]
     
  14. ScottWang

    Moderator

    Aug 23, 2012
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    You may try another way, and you can adjust the R,C values to adjust the time, and to see what happend.

    [​IMG]
     
  15. adamclark

    Thread Starter Member

    Oct 4, 2013
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    thanks, I will try to build the 555 only schematic first, my only question right now is how would any of these work with multiple LEDs? I plan on using 20 blue LEDs to decorate the star.
     
  16. Wendy

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    Mar 24, 2008
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    Here is the From Four, Twenty Schematic...

    [​IMG]

    Eliminate D1 through D8 and the associated resistors, then replace them with this...

    [​IMG]

    Use both schemes at the same time on pins 2,6 of the 555's, the PNP and NPN transistor configurations. You would have both twinkle and fade action at the same time.
     
  17. adamclark

    Thread Starter Member

    Oct 4, 2013
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    That's really what I want.. so do I build the first one just like it is but without d1-d8 and add the lower 2 to it? and where do I add them? How many 555's would I need all together? I want to build this, but im having a little trouble understanding it and how would I connect 20 LED's to this?
     
  18. Wendy

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    Mar 24, 2008
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    The network of LEDs D9-D20 remains unchanged. Just modify each 555 to look like this...

    [​IMG]

    Of course, the LED color is up to you. You can also use one fixed resistor instead of the variable. You can buy Darlington transistors prepackaged, no need to use 2 transistors unless they are in the junk box.
     
    Last edited: Nov 14, 2013
  19. adamclark

    Thread Starter Member

    Oct 4, 2013
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    this is going to get built tomorrow after work,, stay tuned for assistance..lol... and this will do 20 leds without further modification? what does the variable resistor do, control speed?
     
  20. adamclark

    Thread Starter Member

    Oct 4, 2013
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    and pin 3 of the 555 still goes out to the network?
     
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