Powering 21 tiny & 1 small LED bulb for a week

Discussion in 'The Projects Forum' started by GreenFish79, May 24, 2013.

  1. GreenFish79

    Thread Starter New Member

    May 23, 2013
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    0
    Hello Projects Forum! This is my first post!

    I'm in the preliminary stages of a crafts project and am seeking some advice. Because I will be unable to be there for the girl I love's birthday this winter, I want to send her a wooden box (rough dimensions: 12" tall, square base roughly 8x8") containing a "cake" equipped with twenty-one LED "candles" and a surprise message in the box's lid.

    The box will essentially contain three compartments: a false bottom for the batteries and some wiring; a main, central compartment containing the cake, candles, and a switch; and a lid with a false top featuring a pain of dark glass that, when illuminated from behind by a larger LED, will reveal a quote from F Scott Fitzgerald's This Side of Paradise ("At fifteen you had the radiance of the early morning, at twenty you will have the melancholy brilliance of the moon."). The cake will be hollow and ceramic (designed to look like chocolate mousse, her favorite), with ceramic candles that will be hollow cylinders. Wiring will run through the false bottom to the cake's candles as well as to a switch. From this switch, wiring will run through the false lid, behind the glass bearing the quote, to the bulb behind it.

    My intention is to have this circuit running in the mail (likely a few days time, though potentially overnighted) so that when she opens the box's lid, she finds the cake, a birthday wish on it, and 21 burning "candles." The switch would ideally have three positions: one position being the candle circuit, the central position triggering only the message-lamp, and the opposite position being open/off.

    To achieve this, I recognize I will need to wire the two circuits in parallel to the power source. I am wondering what kind of power source to install (AA / C / D alkaline batteries?) and how to configure this power source (total number, numbers in series / parallel) to power these twenty one tiny LED bulbs and single larger LED bulb for upwards to one week (in theory).

    Additionally, I'm open to suggestions about how to connect the bulbs to the ceramic candles. I'm unsure if I can have connecting devices (a standard bulb socket to screw into or a clicking, Christmas light connecting socket) embedded into the clay (will it survive a kiln, I wonder?).

    Lastly, I'm completely open to suggestions about what kind of bulbs and wiring and switch to use -- so if you have anything specific in mind please forward along any links from those products' providers as well!

    Attached is a rough schematic I've thrown together in paint! THANKS FOR ANY / ALL SUGGESTIONS!!

    [​IMG]
     
  2. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    Make the lid the switch so that when it's closed all the LEDs are off. When you open the lid, the LEDs light up. A small magnetic / reed switch attached to the side will work.
     
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  3. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    There is one little problem.

    The bomb squad is going to quarantine your package and blow it to smithereens.

    Then you are going to have cake in your face.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    And I'm not sure that F.Scott Fitzgerald quote is complimentary... ;)
     
  5. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Welcome to AAC.

    How interesting.

    I agree with LDC3, adding a reed switch or just a small momentary switch to the lid or similar will eliminate any need to keep the circuit powered while in transit. Additionally, if you don't expect to keep the circuit powered beyond an hour or two, you can get away with less batteries.

    You can also opt to add a recordable module that plays a song, a message from you, all of the above, etc.

    If you're planning to use one set of batteries to power both the display LED and the candle LEDs, you'll need to either use a wire which will keep the top tethered to the rest of the box or use some type of contacts - no power to the display LED when the top is removed, but no tether. Another thought is to add a drawer to the bottom and place the display there. The batteries could go inside the drawer under the display and it could be rigged so that the display LED comes on when the drawer is pulled out. More complex mechanically, but up to you.

    For the candle LEDs, are you envisioning simple LEDs that are either on or off or do you want the LEDs to flicker? If the latter, is it okay if they all flicker at the same rate (will brighten and dim simultaneously relative to one another) or do they need to flicker independently relative to one another?

    I'm not sure a single LED will be enough to evenly light your message, especially when the height will be fairly small. You could use several smaller LEDs or perhaps a white translucent piece of plastic that is edge-lit by LEDs - this won't be incredibly bright, but it should yield more even lighting across the whole message.

    I'd suggest just epoxying the LEDs into the ceramic candles - I'm not sure you'll find LEDs with screw bases and if you do, they'll be pricey. Alternately, you could use tiny incandescent bulbs which are available with screw bases, but they'll require quite a bit more current and drain the batteries faster. Of course, if you don't need the batteries to last terribly long, these would work fine. Look up something like an E5 bulb/lamp and holder.
     
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  6. GreenFish79

    Thread Starter New Member

    May 23, 2013
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    I think feeding wiring through the candles and simply adhering LEDs to the open candle tops is the way to go. I'm thinking these would work for the candles? And a magnetic switch to control power with a single switch to alternate between candle array and display lamp power is the way to go. For the magnetic switch, I'm thinking this would work?
     
  7. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    It really depends on how big you want every thing to be. A circular arrangement of the 21 candles with 5 times the candle's diameter between the candles would give a circumference of nearly 630 mm or 24.8 in. This is a diameter just under 7.9 in. The cake should be about an inch wider so the cake's diameter is 10 in.
     
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  8. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    As long as the you're planning to make the candle diameter roughly the same diameter as the LEDs (even double would be fine), the 5mm LEDs shown will work.

    Keep in mind you'll need resistors going to each of the LEDs, although I suggest a series-parallel combination - this will help ensure more of the LEDs are the same brightness relative to one another and save you on adding resistors. This will also depend on the type and number of batteries you decide to use. We can help you with the design.

    I'd suggest using yellow or orange LEDs for the candles as these will more closely resemble a candle flame color, unless you're selecting red specifically as part of the aesthetics/color scheme.

    We can help you find sources for parts if you'd like. The magnetic switch you found should work, but some switches are normally open, others normally closed and I didn't see it stated which one this is.

    I'd suggest making up a rough schematic and posting it here before buying any parts - otherwise you risk needing to order more parts which will incur additional shipping costs and add to the total cost of your project.

    Did you decide on whether you want the LED candles to simply come on or flicker?

    You could also opt to use two magnetic switches if you use two sets of batteries and place one set inside the message box. Once the top is removed, the message would light simultaneously with the candles.
     
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  9. GreenFish79

    Thread Starter New Member

    May 23, 2013
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    I was thinking the box would have a base size around 8x8" (less than 1' tall), so I think the bulbs will work well. Thanks for the color recommendation too -- I'll see if I can find orange. I think flickering LEDs would definitely be a nice touch. I'm unsure whether the magnetic switch I found is in the open or closed position when the magnets are connected, but based on the reviews it seems as if the switch is closed when the magnets are separated (based on its instillation in a motorcycle trunk lighting system that's operating the same as my box).

    I have zero experience wiring circuits other than a college physics course on electricity and magnetism (I'll be starting some electrical engineering with circuits and signaling next semester), but I'm assuming the resistors are to equalize current across the bulbs at different locations along the series? Or is it to prevent from blowing the LEDs out in the first place?
     
  10. edwardholmes91

    Member

    Feb 25, 2013
    186
    19
    I'd recommend this LED, they will operate at the same brightness down to 2mA. If you are planning on using 2 x AA batteries that will give 3V supply. with a forward voltage of 1.85V and a 560R resistor in series this gives 2.054mA per LED. Wire them in parallel and with 20 LEDs will give total current draw of 41.08mA. Using one of these Procell batteries you get 67.3 hours of life. That is just under 3 days. Using the D size batteries you get 18000mAH. So that would be approximately 18 days.
     
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