LED Table Border

Discussion in 'The Projects Forum' started by joes238, Jul 29, 2009.

  1. joes238

    Thread Starter Member

    Jul 29, 2009
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    OK so I have a table (7ft long by 3ft wide) that I want to put in an LED Border. the border will be 2 inches from the edge and the LED's will have a 1 inch gap between each. Total there are 224 LED's in the border.
    These are the spec's for the Blue LED I think I will use:
    Typical Voltage (vf) : 3.0-3.4
    Current (mA): 20
    Luminous Intensity (mcd):3500-5000
    View Angle (degrees): 20
    Wavelength (nm): 465-470
    Size= 5MM

    There's a couple things that needs to happen here:

    1) I want the border to have a flashing pattern (maybe more if possible)
    Possible Patterns:
    1) the arcade game where you have to stop the light in front of you
    to win. Like that except with more lights moving around.

    2) random flashing pattern

    3) Any other idea as long as it's visually pleasing :D


    2) On a previous thread by Bill Marsden He had a Diagram of a 555 timer and some 4017 CMOS chips wired to make LED patterns. I need some help and clarification on the parts required and anything I may need for this. I have a general Idea of what needs to happen but could really use some expert advice on how to go about tackling all of this. I figure I'd still go with the CMOS chip design (because its fairly cheap) and I'll get some more hands on experience with components like this (probably more than I want [​IMG]but thats OK ;))

    That's basically everything I think. Here's a picture of a rough copy of what It looks like
    [​IMG]
    Sorry about the giant picture and the crappy drawing (the best I can do)

    If theres anything else thats required let me know and post the info. There's a lot of other components going into this so after I get over this hurdle I'll keep you posted on my progress :D

    Thanks for all your help,

    Joe
     
  2. markosillypig

    Active Member

    Jul 21, 2008
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  3. joes238

    Thread Starter Member

    Jul 29, 2009
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    wow that's really cool. The only questions I have is how did you wire it to single LED's? I understand from the auction that each line can power 100 LED's (and 6 lines will give me plenty of room for tweaking :D) Did you cut off the connections and is there like a positive and negative wire? Does this require resistors or any other parts to put on between this part and the LED's? This seems really promising and something I'll probably end up going with this if i get some more information :)
     
  4. Wendy

    Moderator

    Mar 24, 2008
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  5. joes238

    Thread Starter Member

    Jul 29, 2009
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    so then no resistors are needed in between the actual unit and LED's? that's cool. so as long as I only have 100 Led's per circuit. I figure 3 channels of 74 (last one having 75) That should work out nicely. With that many on a line I should wire in serial right?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    [​IMG]

    Actually, you need at least one. In this design it is a constant current source. A chain only needs one resistor, and the reason this design works is only one chain is on at a time, so you aren't really paralleling resistors.

    For long term reliable use you really do need transistor drivers, which can also be current sources with minor modifications.
     
  7. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    OK so let me try to make sense of this. The item on Ebay. Is that represented by the 4022 Chip in your drawing? How do I calculate the resistor value I need for the beginning of each line? All the stuff before the 4022 Chip I don't need? I'm sorry if I come off a little dumb I'm trying to learn :D
     
  8. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    So I was doing some research and was looking at resistor values and what is needed for my project. For the border if I hook up 3 circuits with around 75 LED's each I don't know how to calculate the resistor value. I found a good Ebay deal and got all my LED's for like $25 (Thank you Ebay:D) and they are a little different:

    Technical Summary RoHS Yes Package F 5mm Packaging bulk Dimensions F5mm Lead Spacing 2.54mm Color blue Brightness 8000 ~ 10000mcd Wavelength 475nm - 480nm Lens Waterclear, White Forward Voltage 3.5V Current Rating 20mA Reverse Voltage (V) 5 Continuous forward current(mA) 20 Peak forward Current(mA) 40 Power Dissipation (mW) 100 Operation Temperature Range() -20~80 Storage Temperature Range() -20~80
    I found a couple resistor calculators that I tried out but I keep getting negative numbers. I think I need multiple mini circuits for each main circuit? Kind of like a branching out effect. I'm just thinking out loud so if I'm wrong then let me know. If anyone could help me with a schematic of some sort that would be highly appriciated. I can do it all myself I just need help with the resistor values and where they go. Also, if I'll need any other components (capacitors and such) for this to be a stable circuit. I have a pending bid on that LED controller suggested above and that will be over around 8 tonight so I'm going with that approach because it seems fairly easy (thanks again for the suggestion :)) Once I get the resistor values set and the actual final drawing done I think I'll be in good shape to tackle this project. When I get home tonight I'll see if I can make up a rough schematic and post it so someone can review it and give me some pointers.
    Thanks,
    Joe
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    I don't have the time to study the eBay item, but it does appear they have done most of the hard work, including the drivers. This is a case of Buyer Beware, however, you won't really know what they are until you have one in hand.

    As a general rule never have an LED without having a resistor. It is a common error we keep seeing repeated over and over, you can't eliminate the resistor. Given that LEDs are 10X more expensive, and one resistor can service several LEDs, it is false economy.

    ******

    The reason you are getting negitive numbers is the circuit won't work. The total Vf exceeds the power supply voltage. You must leave room for a resistor to do it's work, at least a volt, preferably more. This was covered in my article.
     
  10. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    Sorry about not having a schamatic up today. I got home really late from work and didn't have a chance so hopefully tonight I will. I was doing some calculations this morning and found this out. The LED flasher I bought off of ebay is 12V. That means that the output is 12V to each line right? If that's true then the forward drop on my LED's are 3.5 which when I worked it out would mean I can only have 2 LED's in a series. Then at the flasher box I connect all the series circuits I have to one of the 6 outputs and then that should work right? I'll have a crude drawing up tonight hopefully so I'll post that sometime soon.

    Also I was trying to look at the picture and decide how I can connect these up and once I get it in the mail I'll post a good pic so I can get some advice but it looks like there's 2 wires connected to the head so if I take off the connection I'll have a positive and negative wire right? Well that's all I got for now until I get home. Once again thanks for all the help so far :D

    Thanks,
    Joe
     
  11. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    So I made kind of a rough drawing of what I think is right. The resistor calculator said that 3 LED's in series would work with a 82Ω resistor. I don't think it will because the Vf is 3.5 so after 2 LED's there isn't enough for a third. So I went and did the calculation with 2 LED's and it says I need a 270Ω Resistor. The battery is the only thing I could get to show my point but there should b a wire with positive and negative so thats what that is. It's 1 of the 6 outputs I have. And What would happen is I would continue to run the LED series until I reached the end of the border so just image that the chain keeps going until I have about 75 LED's all together.

    The last question I have is what to wire for the last LED in each series. I just run wire to the negative wire from the output right?

    I'm assuming that this will all work so please correct me if i'm wrong or let me know if there is a limit on how many series circuits I can have connected to each output or if I need anything else put on this circuit to make it work let me know. As always thanks for all the help :D

    Joe

    [​IMG]
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    LOoks good from here. When it is working measure the voltage across each resistor. Use ohm's law, plug in the numbers, and you have the current, which you can tweak if you need too. You have the basics down though. The 3 connections on the bottom are connected together.
     
  13. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    OK Then when all my stuff comes in the mail I'll get to work. Just to clarifiy the 3 connections at the bottom (The LED's) are connected do I then connect those connections the to negative wire off of the LED flasher or will it just work with the ends connected to the other ends only?
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The voltage spec's for your LEDs is 3.0V to 3.4V.
    A 12v lead-acid battery is 13.8V when fully charged.
    If you have three 3.0V LEDs in series and in series with an 82 ohm resistor with a 13.8V fully charged battery the current will be 58.5mA and the LEDs will quickly burn out.

    Then calculate the current with three 3.4V LEDs and a weak 11.0V battery. Pretty dim.

    I hope your LEDs will not shine directly into somebody's eyes. They might be blinding.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Joe, were you planning on using a car battery? I scanned the posts, saw one reference to a battery, but didn't see if anything that said car battery.

    Car batteries are designed to provide large surges for short times, they degrade very quickly if you deep discharge them. I'd be tempted to use a small bank of NiMi or Lithium Hyrdride cells (say D cell size) for this, less chance of acid leaks, and they will last longer. Even gell cells, such as is used in UPS's is better, though they also have the voltage variations AG mentioned, since they are fundimentally lead acid batteries. Deep discharge is why marine batteries exist, their more robust construction also makes them more expensive.
     
  16. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    No. The actual plan was because of all the electrical things I'm putting on this table I was going to run a power strip and mount it to the underside of the table since a lot of the things going on this have a cable to plug into a strip. The power source for the LED's was the 12V LED Flasher off of Ebay. The link is right here. The auction says its a 12V LED Flasher with 3 different flash patterns (exactly what I wanted for the border) It says it can control up to 100 LED's on each line and the border has about 224 LED's total so that works out fine too. I figured that was 12V across each line so that's where I got the 12V as my supplied voltage. It doesn't say the output voltage but a simple check with a multimeter should do the trick. Is there something else I should do or need to know?
     
  17. joes238

    Thread Starter Member

    Jul 29, 2009
    21
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    Also just to provide a little more information on the LED Flasher. It has a cord to direct connect to a car outlet so I bought a converter for it so I could plug it into a normal socket on a power strip and the output the converter will dish out is 12V 500mA. That's what I was planning on doing for this portion of the project and once I get the parts in the mail I can test them and see how it works.

    Joe
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    If your 12V converter is not regulated then its output voltage could be much higher than 12V when it does not have a 500mA load. With the voltage too high your LEDs will quickly fry. The 12V from the converter must be 12VDC, not 12VAC.
     
  19. joes238

    Thread Starter Member

    Jul 29, 2009
    21
    0
    I just read the specs and yes it is 12V DC
     
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