flashing leds

Discussion in 'The Projects Forum' started by dd1313, May 23, 2010.

  1. dd1313

    Thread Starter New Member

    May 23, 2010
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    Hello everyone,

    This is my first post.I am helping my grade 6 daughter with a science
    project.I am also new to electronics.What she wants to create is a toy
    (that is her theme).She must use just basic stuff, like LED,battery,resistors
    nothing like 555 etc,

    She wants to create a stage, like the ones the ladies model on.And she will
    place 2 dolls on it.Now the outline of the stage will have flashing LEDs

    Please help me understand how to do it.As far as we have researched,
    connecting the LEDs in paralell is the solution and then connecting them
    to a resistor and then to a battery.

    I have researched that we should ask the electronics store for flashing LEDs.

    Please help me further..

    Thanks
    Devan
     
  2. Bychon

    Member

    Mar 12, 2010
    469
    41
    You seem to have all your ideas correct, to the point that I have trouble finding that you are asking a question. What can I say? Buy the blinking LEDs and start calculating the resistors...or buy the blinking LEDs and ask how to calculate resistors based on what you've bought.
     
  3. dd1313

    Thread Starter New Member

    May 23, 2010
    14
    0
    Thank you,

    If they are blinking LEDs, they don't have to be in paralell do they ?

    And how do we calculate the resistance if we have the LEDs,are all LEDs the same

    Thanks
    Devan
     
  4. Bychon

    Member

    Mar 12, 2010
    469
    41
    Blinking leds will have to be in parallel, otherwise, the first one that goes off will stop all the others.

    To paraphrase your question,
    How do you calculate the resistance if you don't have any LEDs? They are not all the same. You need the LEDs specifications and the voltage you will be using to do the calculations.

    (Power voltage minus the LED voltage) divide by the current needed by the LED = resistance.
     
  5. Bychon

    Member

    Mar 12, 2010
    469
    41
    These are available in 3 colors from www.mouser.com

    They don't need any resistors.
     
  6. dd1313

    Thread Starter New Member

    May 23, 2010
    14
    0
    i truly appreciate the guidance.I will have to checl tomorrow at the store for the ones that I can get.We will be using a 9V battery .How many LEDs can we use please.

    Thank you
    Devan
     
  7. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    9V pp3 batteries have fairly poor capacities so I'd keep it low. 4 or 5 of those Mouser ones would probably drain a battery in a couple of hours.
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Modern LEDs can be hazardous to look directly into due to their brightness, so some caution is required.

    Why no 555's? I assume other logic isn't used either. For simplicity?
     
  9. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    Most blinking LED's do not require resistors in series with them when operated on a 9V battery. You can even connect a different color standard LED in series with blinking LED's and both LED's in the string will blink at the same time. Radio Shack as a several blinking LED's. I would think 10 or 12 blinking LED's would last quite some time on a standard 9V battery, as I have a small pumpkin for halloween that has two blinking LED's that lasts for over a week on one 9V battery.
     
  10. bertus

    Administrator

    Apr 5, 2008
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  11. dd1313

    Thread Starter New Member

    May 23, 2010
    14
    0

    Thanks..

    do you know what they are using here do hold the resistor

    http://www.hobbyprojecten.nl/afbeeldingen/spijker.jpg

    DD
     
  12. dd1313

    Thread Starter New Member

    May 23, 2010
    14
    0
    Yes, it's just to test they know how to apply circuits in practice.
    Nothing fancy.
     
  13. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    The resistor is held at place using a copper nail.
    The advantage of copper nails is, they can be soldered.

    Bertus
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I'm confused a little, you can use transistors but not 555's? Are you wanting runway lights, where they sweep down the strip, or just flashers?
     
  15. dd1313

    Thread Starter New Member

    May 23, 2010
    14
    0
    just flashing lights
     
  16. dd1313

    Thread Starter New Member

    May 23, 2010
    14
    0
    can you connect paralell circuits to form bigger paralell circuits

    Thanks
    Devan
     
  17. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Reading the data (no sheet, just word of mouth) for this Radio Shack Blinking LED it has a Vf of 3-3.8V, so for a 12V power supply at 20ma you would need a 390Ω resistor.

    http://www.radioshack.com/product/index.jsp?productId=2117837#tabsetBasic

    You can put other non blinking LEDs in series and reduce the resistance to get them to blink in time, but the power supply dictates how many. For 12V it is around 4 (including the blinking), for 24VDC it is around 8. LED color affects this, the units we're talking about is red. Other colors drop more voltage. LEDs are current devices, you can not eliminate the resistor in spite of what has been said by others, unless the data sheet specifically says you can (a major exception).

    Just for the record, Radio Shack is not the best place to buy parts. They have a 100% to 1000% mark up compared to most vendors. If you are interested we can point you to some better deals.

    There is no way to sync it with other LEDs without additional electronics, with simplicity comes major limitations. If you're willing to use transistors, 555s or other circuitry you can have real runway lights, but not with LEDs only, they will be at their own rate and pretty random.

    I have an article for other special effects if you change your mind.

    LEDs, 555s, Flashers, and Light Chasers

    I've made true runway lights with some simple circuits, something like this.

    [​IMG]
     
    Last edited: May 24, 2010
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