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Has anyone ever had somthing like this apart?

Discussion in 'General Electronics Chat' started by Andy1845c, Dec 6, 2006.

  1. Andy1845c

    Andy1845c Active Member

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    Take a look - http://cgi.ebay.com/ws/eBayISAPI.dl...MEBI:IT&viewitem=&item=260061478685&rd=1&rd=1

    I have been toying with the idea of trying to build one of these for a while. It would be easier to just buy one, but they are expensive, and I don't learn anything then. I originally was going to use those Sharp LED moduals from goldmine that I posted about a while back, but I haven't been able to come up with a way to get 20v out of my car battery. So they have gone on to other project ideas.

    So.... if I were to try to make my own moduals with LEDs not wired in series, as they are in the Sharp moduals, I should be able to get by on a lesser voltage, right?

    The thing I can't figure out is how I could get the leds so nice and close together and still give them their own resistor. I'm guessing that the manufactured units are able to put lines of LEDs in series since they are made at the same time? Then with a nice PCB things probibly look pretty tidy inside?
    Has anyone ever tried somthing like this? Am I nuts to even think I could pack almost 500 5mm LEDs into somthing and not have it turn out to be as big as a sofa? Are there any tricks to how I could lay out and soldier everything?

    My next question is how bright is a 6000mcd LED? I know thats a bit hard to answer, but I am looking for each segment, (52 LED on the manufactured unit, but mine could use less, or larger LEDs) to be highly visible in daylight.
    I wish radio shack had a better selection of LEDs and actually had some info on the packages, so I could go buy some of differnt mcd rating as see what I like. I hate to order a bunch online and find out there not what I want. Anyone have a recommendation?
     
  2. justDIY

    justDIY Active Member

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    an amber led is a 2v device (on average) ... so with a 14v (12v) electrical system, you can run 6 of them in series and use a resistor to drop whatever voltage is left over

    so your array would be 6 in seres by however many in parallel you feel you need. each series string requires a resistor, not each led.

    6000mcd is fairly dim for an amber led, since yellow/green is in the peak of human vision sensitivity

    you can grab 100 yellow 5mm leds off a popular online auction site for under $10 - that'd be a great way to experiment.

    the easiest way to get daylight visible is to put some sort of glare shield around the light (think led inside a piece of black pvc) ... this way when you look straight on at the led, you see it shining, even if the sun is shining on the display. if the sun is shining in the eyes of the viewer, well, no led will overcome that.
     
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  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The mcd brightness spec number of an LED is meaningless if you don't know its beam angle. Cheap dim LEDs can be focussed into a bright narrow beam by their plastic package, but a narrow beam is useless for anything. If you diffuse it then it will be dim.
     
  4. dave

    Dave New Member

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  5. zevon8

    zevon8 New Member

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    These units are pretty simple, just a whack of surface mount LED's, and some series drop resistors for each group. The controller is most often a simple PIC, programmed to run a few sequences, output is driving a MOSFET, low side switching. One thing to note, the LED's are often not on steady, but are driven pulsed ( PWM ) to achieve maximum brightness while keeping current consumption down. This allows what is known as "day or night" mode, night being a reduced brightness.

    You can do the same thing with a simple oscillator and a up/down counter to get the left/right sweep.

    Honestly, you can't buy & assemble one for the price of a used one. The one in the EBay ad is pushing it at the current bid. I wouldn't pay much more than $100 you're at now.
     
    Last edited: Dec 6, 2006
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  6. Oznog

    Oznog Active Member

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    6000mcd amber is BRIGHT. That's enough to make a decent LED flashlight with. If you look at it straight on, you may be blinded.

    The mcd rating is an average intensity per degree for the specified width of the beam. For a given emitter, a tighter focus will make a higher mcd rating even though the total emitted light energy is the same.

    For a side marker, you do not want a tightly focused beam. In fact in general the typical 5mm T1-3/4 LED package is too tightly focused.

    Radio Shack sells LED tech that is 10 years old. Now there are dozens of popular LED packages that put out 10x the power for 10x cheaper.

    I'm waiting on some white LEDs in a "jumbo" 10mm package. From what I could tell the focus is not tight because they have multiple dies inside there so they can't all be at the ideal focual point. However, the rating is 150,000 mcd!!! Holy schnikes! Not sure how that package can even dissipate the generated heat but that's the rating. The auction went cheap, under $6 for 5 of them and that includes shipping. Gonna be a neat little flashlight.
     
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  7. justDIY

    justDIY Active Member

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    yea, trying to beat china at the cheap game is an exercise in futility ... however, you could build one better or a custom size to fit your application

    quickar has DOT yellow (amber) leds for 10 cents a pop in large quanities:
    http://www.quickar.com/prodview.php?id=76
     
  8. HarveyH42

    HarveyH42 Banned

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    I bought 100 of those couple months ago. They are bright, but not shockingly so. They ar 4 lead pirahna/spider stye, 2.2 volts 70mA. Wired up a LM317 for constant current 64.8 mA, and its been on 24/7 ever since. If you hook them up to a fresh 9 volt battery directly, they blow up. The lense area actually bounced off my 8ft ceiling.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why did you connect a 2.2V LED to a fresh 9V battery?
    Try four of the LEDs in series and a fresh 9V battery.
     
  10. Oznog

    Oznog Active Member

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    LEDs can never be placed on a voltage source without a significant resistance, even if the sum of the LED voltages is near the source voltage.
     
  11. HarveyH42

    HarveyH42 Banned

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    I picked up the wrong battery, thought it was mostly drained and I wanted know which side of the LED was which. I can pick up a regular 5mm LED and tell right off, but these flat, square, 4 lead LEDs confuse me... Just a dim flash was all I needed... and POP! Yeah, I don't do that anymore, that little piece of plastic could have been deep in my eye.
     
  12. Hero999

    Hero999 Banned

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    That depends on the impedanc of the 9V battery.

    I agree one of those little 9V batteries wouldn't be a problem but a large 9V battery used for a transistor radio might blow the LEDs.
     
  13. ZIGGY_DAN

    ZIGGY_DAN New Member

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    Usually the cathode of an LED is larger than the anode if you look at the LED side on, this is to dissapate heat from the LED and indicate polarity.
     
  14. HarveyH42

    HarveyH42 Banned

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    I remember a thread concerning those Sony arrays about a month ago. Search back then and found a site that covered very well. Pictures of it opened up, PCB, and a circuit for driving it. Remember posting the link, but didn't bookmark it. Might have the PDF somewhere on my massive hard drive, but it would be quicker to search this site...
     
  15. Hero999

    Hero999 Banned

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    I thought the large cathode was to act as a reflector, I can't see it being any good at dissipating heat.
     
    Last edited: Dec 7, 2006
  16. Andy1845c

    Andy1845c Active Member

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    Thanks everyone for your replys!

    Do you mean Ebay? I've looked at LEDs on there, but they all ship from Hong Kong. I'm a little leary I may never see them arrive. Anyone had good/bad luck buying LEDs off ebay?

    I kinda figured that, but so far most on ebay with the control head go for far over $100. Even the older halogen units bring more then you would think. I've never figured out why lighting like this is so expensive. These units run close to $500 new. I didn't bid much over $100, so we'll just have to wait and see. The same seller has 2 others on, so who knows how many he has. Its not somthing everyone want, mabey he'll flood the market, lol.

    Do you mean they are pulsed faster then the eye can see, so as to create a steady on look? I never thought about that. Interesting!:D

    Wow..... are these off ebay too? Let me know if they are really that bright. I'll have to see if i can get a few:)

    lol, sounds tempting to waste a dime and try that...... j/k

    That was me you posted that for:D I have it safely tucked away on my harddrive. The problem I ran into was getting the 18v required, for the green leds, from my car. I found all kinds of stuff on DC/DC Boost converters, but other then the 500ma ICs, the rest was over my head at the moment.
     
  17. HarveyH42

    HarveyH42 Banned

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    http://besthongkong.com/

    I've gotten a few hundred LEDs here. Shipping is very cheap for overseas, takes about a week.

    If you blow up LEDs, wear eye protection, serious threat. Not sure if it would penetrate the skin, maybe if its sharp. Should sting a little.
     
  18. Andy1845c

    Andy1845c Active Member

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    Only a week from Hong Kong? Seems like it takes almost that long to get somthing from the west coast to Minnesota. lol I've browsed besthongkong alot, seems like the prices are pretty good, but I wondered if the quality wasn't so great or somthing. Mabey I'll give them a try somtime.

    As interesting as it soounds to blow up leds like that, I think i'll refrain. lol I'd feel kinda bad senselessly killing them;)
     
  19. Andy1845c

    Andy1845c Active Member

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    Well, i'm outbid:( Oh well, now I can get back to dreaming up my own custom design I guess.
     
  20. justDIY

    justDIY Active Member

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    I recently purchased a bunch from someone in Pennsylvania, and they cost less than the ones from HK. ebay has a feature to filter out the Chinese spam, set your location filter to "North America".
     
  21. Andy1845c

    Andy1845c Active Member

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    :eek: :eek: :eek: The auction just ended for $222! An identical unit went for $255 5min earlier.... I guess I was dreamin' at a hundred bucks:rolleyes:
     

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