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Blinking LED Bottle Light Chandelier

Discussion in 'LEDs and Optoelectronics' started by Mr. Oddly Fox, Jul 24, 2015.

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  1. Mr. Oddly Fox

    Mr. Oddly Fox

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    Jul 10, 2015
    Sounds complicated and exotic, I know. Just stick with me here.
    I am building an LED chandelier and I want it to blink.
    I will use a switch to turn off the light, and a switch to enable/disable the blinking function.
    I have also attached a quick sketch as to how I want the switches to perform.

    The chandelier will incorporate 10x 0.5W, 120mA LEDs with forward voltages of 3.6V.
    The power supply is 5V/2.5A.
    I only want to bring the power down enough to not burn the LED out.
    I need them as bright as possible without destroying the component.
    I usually use this to calculate the right amount of resistance, but since most of the blinking circuits use multiple resistors, I am at a loss.
    http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

    There are two basic blinking circuit configurations that I know of; attached.
    I want to keep the LEDs as bright as possible, but make them blink.
    I was thinking about making a board with 5x paired LED blinking circuits; but I am open to the idea of every light having it's own blinking circuit using the single LED configuration.

    My biggest issue is the resistance. Since these circuits incorporate different components and multiple resistors, I am having an trouble comprehending what to do.

    And if I could get some advice on transistors, I have had some issues reading their specs. (maybe my source was bad)
    - How are their limits measured?
    - How much voltage is too much?
    - Do they have current limits?

    And if you have any ideas as to how to make 10 LEDs blink randomly, I am open to suggestions.
    Like if one LED could blink every 0.5 seconds, another could blink 0.7 seconds, and another 0.9 seconds, and so forth.
    I want the offsets to make the blinking appear random and not so predictable to somebody watching it.

    I want to say in advance, thank you. I really do appreciate the help I receive on this forum.
    led1.gif t-flash2.gif
    20150724_141124.jpg
     
    Last edited: Jul 24, 2015
  2. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    The transistor in the first pic is backwards...
    You can do this one of two ways... discrete components, which would require a flashing circuit for each LED or each set.
    Or a microcontroller... The microcontroller approach will keep component counts down, and will let you make adjustments on flash rates, flash pattersn/styles/etc without having to rewire the whole thing.

    Now.. the 'flashing', are you after a 'twinkling' affect, or just a simple on/off? How many LEDs? Is it ok to have 2 or 3 LEDs operate exactly the same? (perhaps if they are in different areas on the chandelier)
    At any one time, do you want half the LEDs on, and half off? Will they be mostly off, flashing on? or mostly on, flashing off?
     
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  3. Mr. Oddly Fox

    Mr. Oddly Fox

    19
    0
    Jul 10, 2015
    I think that I am interested in more of a blinking effect, with more on than off, but balanced. Trying not to have more than two off in a row. Two on in a row is fine.
    BUT, that twinkling makes me think of almost like a fade on, fade off. That would be most excellent.

    How does the microcontroller idea work? How would I design that kind of circuit?
    I do apologize if I don't seem like I know too much.
     
  4. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    The microcontroller approach would take a bit of planning, but you would essentially take an output pin from the microcontroller and connect it to a transistor. The transistor will be responsible for turning the LED on and off.
    The catch here though is this:
    Creativity with the programming... You can't just set each pin to blink, you need to write your program to toggle the pins on and off... You can either program in a specific pattern that repeats, or make the program blink them randomly.
    There is a limited number of pins on a microcontroller, so if you want to control more LEDs than pins, you will need to pair up LEDs to run more than one on a pin, or use an additional microcontroller.

    (There are more complex programming methods such as multi-plexing, but we may not need that depending on how many LEDs you will be using in total.)
     
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  5. Mr. Oddly Fox

    Mr. Oddly Fox

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    Jul 10, 2015
    Whoa. That sounds complicated. And I see that it requires additional equipment. I will have to save the microcontroller project for another day.

    I think I will shift back to the component method. Capacitors and transistors.
    What determines the blink timing is the capacitors, yes?
    How do I select a transistor? What kills transistors; I want to know more about them and how to keep them safe.
     
  6. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Well.. to be fair, it would probably use less hardware than the other method.
    Look at 'arduino' . That would be a replacement for many flashing circuits, and only requires a USB cable to the computer to initially program.

    Now.. as far as flash rates are concerned, the value of a capacitor in Farads, and the Resistance will determine the 'RC time constant' which will dictate flash rates. The second image in your very first post will flash back and forth and is a very simple design for kid's police toys.
     
  7. Mr. Oddly Fox

    Mr. Oddly Fox

    19
    0
    Jul 10, 2015
    It is an interestig method, but I have a bit of a schedule to keep. Using components is easier for me than programming a controller.

    How do I select a transistor? How do I know which resistors to use without making the light dimmer? With a 5V power supply, I have been using a single 12 ohm resistor for a single LED. And that was selected by the calculator I use normally, but this is different. Does the transistor need a specific resistance? What kills the transistor component?
    so many questions!! Apologies.
     
  8. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    No worries. This is not a terribly unique project, so a very vast array of transistors can be used with success for your project.
    Depending on the flash frequency you use, the transistors may be operate in the a 'linear' region for a small time, which will cause heat to build up. The amount of heat is directly related to the current draw of the LEDs and the voltage across the transistor.
    Using darlington pairs will cause the LED's to switch faster which will reduce the time spent in the linear region.
    When choosing transistors, try to find the current rating and make sure you are under that limit ;)

    What kills transistors is stress, overheating, or improper use... for example, reverse polarity, electrical noise, too high a voltage from any two pins.
     
  9. Mr. Oddly Fox

    Mr. Oddly Fox

    19
    0
    Jul 10, 2015
    Can you recommend a transistor for this project? It will most likely be outdoors, so I will probably have to enclose the circuit board. So 10 transistors on one board, covered up. Sounds like trouble.
    And how do I get the rating under the limit and not effect the LED brightness? Or do I just get one rated high?
     
  10. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    A 556 timer driving four short strings of LEDs via 2N3904 transistors would be my suggestion for a design without a microcontroller. I'll post a video later showing two of these running densely packed LEDs.
     
  11. Colin Mitchell

    Colin Mitchell

    1,417
    312
    Aug 31, 2014
    Get yourself a red blinking LED and look at it.
    If you like the flash-rate, use it to blink all your other LEDs.
     
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