Help with multiple LED Circuit

Discussion in 'General Electronics Chat' started by dog812, Feb 27, 2009.

  1. dog812

    Thread Starter New Member

    Feb 27, 2009
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    Hi
    I make LED Hula Hoops for my GF and her friends. LED Hula Hoop

    Currently, if you check my DIY section of my site, i use 4 x AA rechargeables in series to light up the 21 LED's and have a external plug in style charger.
    Making the hoops expensive.

    I am trying to come up with a way to power the 21 LED's with a single AA or something. that they can put in and remove out of the hoop themselves.. Making them cheaper to build and maintain.
    Is this possible?

    What other options do i have?
    Remember this circuit must fit inside a 3/4" tube.

    Any info would be greatly appreciated.
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    If you use a perfect voltage boosting circuit then a single battery cell will power the LEDs for 1/4 as long as 4 battery cells. But the voltage boosting circuit is not perfect and it wastes some battery power so a single cell will last 1/5th as long as 4 cells.

    Rechargeable batteries have plastic insulators inside. Soldering to them might destroy them.
     
  3. dog812

    Thread Starter New Member

    Feb 27, 2009
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    Where do i get this voltage boosting circuit?
     
  4. Barry M

    Active Member

    Feb 11, 2009
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    Im posting this to see if I got it right, so dont use this until someone says it looks fine. Theres only 3 LEDs but they are in paralell so you can extend to your desired amount.

    [​IMG]

    It should (haha SHOULD) work, i think and have 2/3 modes. On or off/charge mode. Also this is for 2 X 1.2V rechargable batteries and not 1.5V throw aways.

    You might have to use resistors on some of your LEDs, others may not require any.

    Just remember Im only learning so this is as much a question for me as you and dont use it unless someones says its ok ... remember resistors too.

    Edit: I think keeping them rechargable is the way to go because when you think about how long they take to make and the wear and tear opening and closing the hoop for throw aways makes. Keeping it a sealed unit I think is probably better and one less thing to worry about breaking down.
     
    Last edited: Feb 28, 2009
  5. pkennedy

    Active Member

    Feb 27, 2009
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    maybe you could add one resistor before the parallae leds to limit current flow but the led is a diode and will require a set voltage to begin to conduct depending on the size of the leds the one battery may not last long at all .maybe try a 3v lithium ion rech.battery it will give a bigger source voltage and extend the operating time.
     
  6. pkennedy

    Active Member

    Feb 27, 2009
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    I just checked your sight those hula hoops are pretty cool looking good work
     
  7. pkennedy

    Active Member

    Feb 27, 2009
    44
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    this is just a suggestion but you could build a simple circuit to get those bad boys blinking
     
  8. dog812

    Thread Starter New Member

    Feb 27, 2009
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    0
    You can buy blinking led's. Same price..

    The reason i was looking at joule thief's is i want to make these cheaper for the girls.. A single AA rechargeable that is readily accessible would be ideal.. possibly 2 AA's.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    A Joule Thief circuit dimly lights a single LED. Like a solar garden light. It is barely visible unless it shines at you in the dark.

    Your circuit has a supply of 2.4V and will not light bright green, blue and white LEDs that need about 3.4V. Each LED needs its own current-limiting resistor.

    When you stepup the battery voltage then you are also stepping up the current so the battery will not last long.

    You do not need a two-pole switch. Use a single-pole switch to switch the battery's positive wire to the LEDs or to the charger. Then the negative of the battery, the LEDs and the charger are all connected together.
     
  10. dog812

    Thread Starter New Member

    Feb 27, 2009
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    the 2 pole switches were cheaper at that time.. i have since switched to single pole.
    And what you explained is how i have it hooked up.. see my 21 led diy... step 8 i thnk has a diagram of my wiring.

    So your saying the joule thief will not work for my application?
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    718
    The joule thief could work with a large enough toroid and enough turns, but it would be very inefficient. It is great at running cells down to 0.5V, but wasteful with a new battery. However, it is about the simplest and cheapest boost circuit one can make.

    There are several boost ICs available for $2 - $3 that need only a capacitor and/or inductor, and will provide the voltage/current you need with a source voltage down to about 0.9v. That limit will keep rechargeable batteries working longer, compared a deep discharge every cycle. Maxim's Surface Mount Max1642 is good for single cell low current applications, with 83% efficiency, over double the efficiency of a Joule Theif, and the entire circuit would fit inside the hula tube.

    Here is the datasheet:
    http://datasheets.maxim-ic.com/en/ds/MAX1642-MAX1643.pdf

    It is a decision of cost of components, frequency of recharging/replacing batteries, as well as how many cycles a rechargeable battery will live through.
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    What is wrong with this site? It takes many minutes for it to wake up when I try to reply.

    The tiny MAX1643 has a max output current of only 20mA which is good for only one LED.
    But the hoola-hoop has 21 LEDs.
     
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Good point. I was comparing to Joule Thief and lost track of current draw.

    Other IC's exist for similar inputs, and higher outputs. Dissipated power would be the main consideration due to the lack of airflow inside the tube.
     
  14. dog812

    Thread Starter New Member

    Feb 27, 2009
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    thanks for the info..
    I am still really new to this stuff and reading as much as i can.
    Hopefully i can find a circuit that will work for my application that will help me bring the cost of these hoops down.
     
  15. mistydake

    New Member

    Dec 7, 2009
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    I too make LED hoops and have been looking for a way to power them with a single battery and there is a site called trickconcepts.com that makes a single battery hoop with a 3.7v lithium ion rechargeable battery that is removable and has an external battery charger. I think they must use springs like in a flashlight and you drop the battery in the connector and when you connect it it completes the circuit. lithium chargers can be expensive but the ability to just change out a single battery when your hoop starts dying is priceless.
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    I don't know where you get dim part of the joule thief, but the ones I've seen are pretty good, as in bright, lighting a white LED to the point it compares favorably with a small flashlight. I would try building a few to see how they work for you. It is possible the Walmart specials I've been buying for $3 use something else, but the single AAA battery has good life and a bright white LED.

    The life will be shortened with extra LEDs, but then you also get to use AA batteries. You could get the Walmart units and see what the innards look like.
     
    Last edited: Dec 7, 2009
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