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  #1  
Old 08-22-2010, 08:09 AM
acefire acefire is offline
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Default LED Tile Wall (Micro Controller Help)

Hi i have posted in The Projects Forum but i thought it may reach people quicker if i posted a small amount in here about the MC side of the system.

Here is the basic rundown so far
Hi there, i am a beginner when it comes to electrical circuits but i am a motor vehicle engineer so i do understand how to diagnose problems and understand V=IR to some extent.
Quote:
What i am pondering to make is a wall of Acrylic frosted glass with a Tri-Colour LED behind each tile and also a white LED behind every tile also. I am thinking it will be around 42 of Each type of LED as it should be around 42 tiles (Around 20 CM2 each) I am looking to get the tiles connected to a pc so they can be controlled by a program hopefuly Visual Basic as i understand VB but if not i will have to learn the other languages. I want it so any individual LED can be turned on and off so the wall can be whatever design is chosen through the program. I have looked into Arduino boards but i do not know if these wold have enough pins for me to make this possible.

I am looking into High power white LED's and 5mm or 10 mm Tri Colour LED's also that would be bright enough to light up the 20cm square.

I would appreciate if someone could give me an idea of what i would need to make this possible and any educated guess at a price range for it all (ignoring tiles ect, only electrics) Also things like if i would need a resistor seperate for every LED or a way to do it so they can all run from a smaller amount.
What i dont really know is what type of ucontroller to use i have looked into Picaxe and i think it may be possible but do not know the right one to go for or if i have to just get a chip or if i can use the experimental ucontrollers on the website.

Thank you.
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Old 08-22-2010, 08:39 AM
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debjit625 debjit625 is offline
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In simple way I would do it using multiplexing you need a microntroller of just 14 output pins i.e.. 8*6 = 48 and thats more than 42.

Good Luck
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Old 08-22-2010, 08:52 AM
acefire acefire is offline
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Ok sounds good, could you go into any detail for what i would need to multiplex? And would it let me control any led at any time?

Thank you.
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Old 08-22-2010, 12:53 PM
tom66 tom66 is offline
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Is this similar to your project?

http://www.scotttorborg.com/disco-da...oor/index.html

If I remember correctly, they controlled it using .NET.
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Old 08-22-2010, 02:50 PM
acefire acefire is offline
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Yes this does seem very familiar to mine but mine is quite a lot smaller than this design. Shame they do not post much helpful information.
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Old 08-22-2010, 03:33 PM
wannaBinventor wannaBinventor is offline
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Quote:
Originally Posted by debjit625 View Post
In simple way I would do it using multiplexing you need a microntroller of just 14 output pins i.e.. 8*6 = 48 and thats more than 42.

Good Luck

I disagree with this because the tricolors are going to have three leads versus two. I'm guess two anodes and a common cathode.
1 anode will be one color, 1 will be the other color, and both will be the third color.

Then I think you also wanted a white LED. So thats a total of 84 cathodes. With the TRi-colors and the white LEDs, you are looking at 84+42 = 126 anodes. 84 + 126 = 210 pins. You could also consider a multiplexer IC or some data buffers to lower your uC pin requirements.

You're an engineer, so I'm sure you can come up with optimum arrangements/pin requirements from here.
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Old 08-22-2010, 04:02 PM
acefire acefire is offline
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Im a motor vehicle engineer not an electrical engineer. But do i need the "earth" side of the LED to go back to a pin? would it not be possible to just use a joint earth for all pins going straight to the negative side of the power supply and just use the anodes as pins?
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Old 08-22-2010, 04:42 PM
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This is a pretty good description of multiplexing, should get you started.
They use a counter chip but you could use 8 more output pins for their application.
You have 168 (42X4) LEDs so it will be more complicated.
This could be thought of as 12 rows by 14 columns, so 26 pins required without using a counter. However the LEDs would only be on 1/12 of the time which could make them very dim. One method is to increase the current to them - LEDs can take more current if it is only for a fraction of the time (check the datasheet). <ed> You have to be very careful with this method because if yuor code goes wrong you could burn the LEDs. </ed> The other way is to use more pins and make a 6 row by 28 column array or an 8 by 21.
http://www.best-microcontroller-proj...x-display.html

Last edited by Markd77; 08-22-2010 at 04:48 PM. Reason: disclamer
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Old 08-22-2010, 04:46 PM
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Ok I missed that its tri color and one white extra so every set will give 4 connection and a common ,so make 7 set of 6 tiles and multiplex it,every set will need 6*4 = 24 pin and plus 1 for switching the set ,i.e.. for all the tiles you need 24 + 7 = 31 pins on a mcu to multiplex.

For know about the process of multiplexing do a google search ,I did it and found some here is one http://www.winpicprog.co.uk/pic_tutorial13.htm

Good Luck
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  #10  
Old 08-22-2010, 05:39 PM
nickelflipper nickelflipper is offline
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Many popular microcontrollers can only source 200-300ma maximum current. The power budget could easily be exceeded, especially if higher power led's are selected.

They make led drivers that handle adustable constant current sourcing, without the need for individual resistors, and include individual pwm control. If full brightness is not required, then a multiplex board like the Rainbowduino, would easily handle your requirements.

Consider the more expensive plcc6 rgb leds by Osram or Cree for beautiful color mixing and wide angle dispersion for your 20cm2 tiles. If those aren't in the budget, then at least some other wide angle types, like the straw hat or piranha.

Last edited by nickelflipper; 08-22-2010 at 05:44 PM. Reason: max chip current
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