Out of my depth whilst standing in a puddle- Help needed

Discussion in 'The Projects Forum' started by Bananas, Oct 8, 2008.

  1. Bananas

    Thread Starter New Member

    Oct 8, 2008
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    Hey guys,

    Im a student and for an upcoming project I require some simple electronics to fit into a glowing presentation box. Sadly electronics is not my field (at all!) and Im having trouble piecing together a fairly simple operation.
    My field is in 3D/interactive graphics the box Im making will be used to hold a DVD of some of my work. I already have the box designed, I just need to make the circuit to go inside it to make it glow..... but I dont know how?:confused:

    Here the deal:

    • The circuit is for an 8 LED set up that will fit inside an acrylic translucent box.
    • There should be a switch with three options On/Off/Motion. On and off are self explanatory, motion willl be for when the box is moved, with a short delay to it turning off once movement stops.
    • The box will be in two halves connected only by magnets, I require lights in both halves, these can be on the same circuit. i.e the lights go out when the box is split. If possible using the magnets as a part of the circuit... or if not I'll have to use a normal connection.
    The next section is all guess work: If someone could be kind enough to help me fill in the blanks.

    I will need 8 very bright LEDs(4 in each half), these can be either Blue or tri colour(red/blue), size=any? whats the difference except the obvious? How do I then calculate resistors and battery size?

    For the motion sensor; I guess a tilt switch is needed??? Im not sure how these work or even if its the correct component(Yes Im out of my depth?).

    I then need to piecie it all together with a switch.

    Basically could some kind soulcould help and mentor me in building this circuit? What infomation do I need to provide for a better understanding(No not my credit card number:p)

    thanks in advance

    Bananas
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    None of this sounds too impossible. The sticking points are a definition of "very bright" and "short delay". This sounds as if batteries are the intended power source, so LED intensity and battery life are closely related, unless weight is no object.

    What are the box dimensions and material?
     
  3. Bananas

    Thread Starter New Member

    Oct 8, 2008
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    The very bright; is 'as bright as they come', the acrylic will be opal translucent and 5mm thick so the LEDs would have to be powerful enough to illuminate the box even in daylight conditions. If 5mm is to thick for an LED it is possible to reduce thickness to 3mm.

    Weight: Not to much of a problem, I'd like to try and keep it under 500g total but the look is more important than the weight.

    The delay:The idea is that it is a plain white acrylic box, when the user picks it up it will illuminate and continue to illuminate whilst being handled, when they put it down, it will wait 20 seconds before turning itself off. I'd also like it to have a switch so that it can be turned permanently on or off for display and carriage purposes.

    The box dimensions are 130x130x130mm. The box will have two large cavities(top&bottom) 120x120x50mm in size, this is where all electronics can be housed, the idea was to have the batteries mounted on the underside of where the DVD sits so that they dont cast any shadows. To try and keep it simple Im happy with plain blue LEDs however I'd love it to cycle through different colours.

    I've attached some rendered images, I have left the lights on consistently in the pictures even when the box is in its two seperate sections, however in real life this will not be necessary(although come to think about it would be pretty cool, I guess it require 2 circuits).

    Any further ideas or development on how the box should/could work is welcome.

    Any help on how to do the electronics would be appreciated.
     
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  4. thingmaker3

    Retired Moderator

    May 16, 2005
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  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    This might be a good source for blue LED's - http://www.allelectronics.com/make-a-store/item/LED-122/BLUE-ULTRA-BRIGHT-LED/-/1.html. The price is very good. I have paid over $2.00 for similar ones not too long ago. From your metric dimensions, you may be on the other side of the Atlantic. Try a Google search on "ultrabright blue leds".

    I would stay with blue because the color is unearthly, and attracts attention. Also, I have yet to see another color LED put out similar light intensity, although there is an orange that is about as hot a color as you could imagine. Stay with clear LED's. Not so much because they are brighter, but they are easier to orient when making connections.

    There are tilt switches readily available, and a simple LM555 timer will most likely do for you motion activation and time delay. Have to think a bit on the magnets. It would be nice to use magnetic reed switches to activate the boxes when separated, but using magnets to hold them together presents a problem.
     
  6. Bananas

    Thread Starter New Member

    Oct 8, 2008
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    Thanks thingmaker3 for the links, I had seen those multi coloured LEDs, the problem I have is that I dont even know how to properly wire a uni-colour LED just boggles my brain further. Im in real need of a laymans walkthrough.

    Im in the UK. Rough conversion the box is a 5" cube, the disk bay takes up about an inch leaving about a 2" cavity either side to fit the electronics.

    Okay if I can say with certainty I'll use blue, does the size matter? Ive been looking at rapidonline to try and get an idea of what I might need, I will shop around for prices once I have a full list together. They have LEDs available in 10,8,5 & 3mm, are bigger brighter? I assume more are better as I want this thing to really glow:) How many would be feesible? battery life not being to important.

    *goggles magnetic reed switches*
    How do you see these working in the design? Are you saying the other magnets would interfere with switch?
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    As far a LED's go, the larger the output, whether lumens or millicandelas, the better. There do seen to be more choices in the T 1 3/4 size (5mm).

    If you want to do some experimenting grab a couple. Follow this link - http://www.allaboutcircuits.com/vol_3/chpt_3/12.html - into our Ebook to see how to run a LED. That might be of interest to you.

    If you can use NiMH calls, battery life should be no problem, but we'll get there...

    I was thinking of reed switches to indicate when the boxes were separated. Each would have a complimentary magnet in the other box, and would open when the magnet moved away from it. But, using larger magnets to hold the boxes together make that idea a bit iffy. We'll think of something. To what degree and what degree of alignment is going to needed in joining the boxes?
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    Ordinary little LEDs are made to dimly light a garden light at night. Ordinary little narrow angle LEDs will not light your cubes in the daytime. High power wide angle Lumileds will.
     
  9. Bananas

    Thread Starter New Member

    Oct 8, 2008
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    Im not sure if I follow this section, the magnets will have to be strong enough to lock the two halves together. If it becomes to complicated and I can either have a second independant circuit in the top or I was thinking of a small spring and a plate alongside one fo the magnets to effectivly act as a switch.


    I had read through the ebook and am getting a better understanding of LEDs.

    I have also been reading stuff from other circuits and sources and I keep seeing switching and linear regulators to control power flow. Would my design benefit from one of these?
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    At the simpliest level, all a LED requires is a resistor. As you increase complexity, such as numbers of LEDs you need more control, but I suspect you don't really need to go beyond a resistor for your application. What batteries are you thinking of using? Are they going to be rechargable?
     
  11. Bananas

    Thread Starter New Member

    Oct 8, 2008
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    This is where my ignorance of electronics will show and why I need help.

    The batteries will be whatever is necessary and easily available, AAAs, AA, button, 9vPP3. If it is less than 1.5" wide and will fit within the size of a CD(4"x4") it can be considered. It does not have to be recharable and battery life should be a good few hours(4+).

    My initial thought was to use a pair of AAs, but this is not a technical decision just a convenient one. I dont know if that would be enough to power 8 LEDs to the brightness I require..... I dont even know if 8 LEDs would be enough illumination or if I should use more to be on the safe side, I only calculated 8 based on the number of corners in a cube.

    If I were to use 2 AA bateries how many bright blue LEDs could I power from it?
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    You'll need at least 3 1½V batteries, probably AAA. This is because blue LEDs need higher than normal voltages to turn them on, after which the amount of current determines brightness. If you use rechargables you'll need at least 4 batteries, as a rechargable runs around 1¼V. AA will last a bit longer of course.

    I'm talking minimums here. You could go with 4 regular batteries, or a 9V. I like the 9V option (though it won't last as long) because you can use the extra voltage for electronics. The AAA or AA will last a lot longer though.

    There isn't a max number here, it's like lights in the house, just add units in parallel to get as many as you want. The more you have, the shorter the battery life. The bigger the batteries, the longer they last. If you could fit C cells then you'd get even longer life.
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
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    Two AA's will give 2.4 volts if you use NiMH, about 2.5 for NiCad. Not really enough for blue LED's, which take around 3 volts to run. Three AA's would be better. After they have enough voltage to start conducting, it's just a matter of controlling current.

    My guess is that your box will illuminate best with blue light, but white could also work. In 5mm sizes, the white LED's are usually blue with a layer of a material that scintillates yellow over the die. The characteristics are the same for those LED's, but the light output is less.

    Once conducting, an individual LED wants something on the order of 10 - 20 milliamps os current. Intensity varies with the current, so figure on the high end. For 8 LED's and 20 ma each, that's 160 ma. A set of 1800 mahr NiMH cells should run around 10 hours with that level of current.

    I finally read closely enough to see that you simply wand the lighting circuit disables when the box is open. One of those locating pins can probably do that by opening a switch.

    Have you some extra material to investigate lighting effects with LED's? It would be best to have the LED's in the lower portion, so no wires need be run to the top. It might be interesting for you to obtain a few blue LED's and experiment.

    I have done something a bit like this with neon lamps. Rigged with big resistors and small capacitors, they flash briely and somewhat randomly as a set of relaxation oscillators. I have them mounted in slabs of plexiglass, poked into drilled holes of differing depths. The outer surfage of the cude is frosted, so the flashes have a bright center, but light up the whole block as well.

    The question is: how well does your opalescent plastic conduct light across a gap?
     
  14. Bananas

    Thread Starter New Member

    Oct 8, 2008
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    A 9v sounds ideal for size, however I have read and Im not sure if this is correct(I may of misinterpreted it) that they loose the initial strength quite rapidly, so maybe I'd get 30 mins of very bright light followed by ??hours where the current is weak! Do you know if this is correct?

    At the moment Im torn between a 9V or 4x AA depending on the above^

    A C battery cell would fit in the box but I feel it is a little to large and heavy. Although I'd like to factor battery life into any equation I feel that a couple of very good hours would be far better than many hours if compromising or considering weight, shadows, brightness etc..

    Unfortunatly I dont have any materials to experiment with, I live in a very rural area and the only store that sells LEDs is expensive ($5 per LED). Acrylic is also proving difficult to get hold of at a reasonable price unless I want huge sheets of the stuff, I hope to find some in the next week when I go into the city, if not, I'll have to order it online and take a risk with the translucency. Same with the electronics if I get everything at once I'll save on shipping, Im a student so I must keep costs down, I dont mind spending money on components if its within reason and at the moment it looks cheapest to order from either the US or HK. Crazy world!

    If I plan meticulously and make sure I cover for any mishaps or alterations it should be okay, thats one of the reasons the more LEDs I can fit on the circuit and the brighter I can get them the better. Even though Im finding the whole electronic side confusing I dont believe it is too complicated so once I understand the circuit it should be fairly straight forward.
     
  15. beenthere

    Retired Moderator

    Apr 20, 2004
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    Are there suppliers online you can order from? I just got a couple of bags of run-of-the-mill 3 mm LED's from a supplier here for about $.02/ea. Ordering parts is going to be much more economical. And you can't get a lot more rural than where I live.

    I have just attached a schematic of the timing circuit that will give you 20 seconds of light when the switch is closed.

    Now I just have to hit the catalogs and see if I can find that tilt switch again. I do have some old mercury filled capsule switches from several thermostats that would work pretty well, but there is several grams of Hg in each bulb. Won't go over well with guests.
     
    Last edited: Oct 10, 2008
  16. Wendy

    Moderator

    Mar 24, 2008
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    I have to agree, LEDs can be had very cheaply, with just a little shopping. I'm assuming this circuit beenthere came up with is run off 3XAA batteries. The LED resistors seem a little low, but it would work, and be bright. You might ask other members here for part outlet ideas in the UK.

    Some of the other values got cut off the attachment too.

    [​IMG]

    A 9V battery could work, but you'd have to go with regulator circuitry, the 3XAA is simplier in the long run, and will have much better battery life.

    Several technical questions at thingmaker, where is the pull up resistor for pin 2? I thought that was required for this kind of circuit.
     
    Last edited: Oct 11, 2008
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