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Project Help and Ideas » Wonderful 5x4 LED Array!

May 19, 2012
by Pew446
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I've been working on this one for a while, with a lot of help from the Nerdkits forums. I have to say, this would never have been possible without the things I've learned with my NerdKit.

What is it?

A 5x4 LED Array that uses a total of 5 pins on the microcontroller. How is this possible, you ask? Charlieplexing. Charlieplexing is an efficient but rather complicated way of arranging LEDs in a way to use the least pins while having the most LEDs. The equation is #LEDs = #pins*(#pins-1). By turning one pin high, one pin low, and the other pins to input, I am able to turn on a specific LED. Charlieplexing is more efficient than Multiplexing, the way the LED Array Nerdkit is created. If you wanted to multiplex a 5x4 Array, you would need 7 pins, whereas with charlieplexing, you only need 5.

What does it do?

Pretty much the same thing the original LED Array kit does, although I only had about 2 days to code it, so it's missing some things such as scrolling text and being able to take feed from the computer. So far it displays the entire alphabet, a transition pattern, and a simple "Hello World" phrase.

Why did you do it?

Because I love learning and wanted to expand my knowledge from the things I've learned with my NerdKit, and also because we had to create projects for Engineering at school (due this Monday!), and I thought this would be an awesome project.

Well, that's nice and all, now show me it!

Okay. :)

The guts before they went into the case!

The charlieplexing!


The big ol' case! (Radioshack didn't have any smaller cases :P)

The video! (I forgot to mute it and I'm too lazy to re-upload it. :))

Please give honest feedback! I want to start selling kits like these to teach people how to charlieplex, so I need your opinion on what to change, etc.

Also if I forgot to say anything, ask and I will answer.


May 20, 2012
by pcbolt
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Nice going PEW446.

Next step would be to add shift registers for expansion. Or if you're really brave...go 3D.

May 20, 2012
by Ralphxyz
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PEW446, I notice some of your leds are distorted or blink like led 5,2.

Is this because of the charlieplexing (which is very cool)?

I have been dreaming of a 3D LED cube ever since I did the Nerdkits LED Array.

This is really a great project.


May 20, 2012
by Pew446
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Ralph, In order to create a solid look to the human eye, I had to blink each LED individually at a rate of ~1 ms (actually it could be achieved with a bigger number, I just chose 1 ms). In the video it appears to blink because the camera has a faster frame rate than the eye, but in real life it appears completely solid.

As for some of the LEDs being distorted or appearing not as bright as the rest, that is because I drilled the holes with a hand drill and messed up a few times, so some of the LEDs aren't straight. :P

May 20, 2012
by dvdsnyd
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Hi Pew446,

Very cool project! You must have put a lot of work into it yesterday when you got your new microcontroller :-) The only thing that I would say as a negative...and there isn't really anything you can do, unless you wanted to make it bigger, is some of the letters looked kinda similar to one another. Like, V and U, W and maybe a couple others. But in actuality, it probably is better than my own handwriting any day :-p I say go 3D like pcbolt said :-D Once again, great job! Hope you do really well on it for your class. Keep it up!


May 20, 2012
by Pew446
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Thanks David! Yeah I had some troubles making the letters distinguishable, but I figured people know the alphabet well enough to know what comes next. I plan on making this array bigger this summer. Also, I've never attempted to go 3D, sounds really fun!

May 24, 2012
by RogerFL
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Nice work Pew. But all, what do you mean 3D?

May 24, 2012
by pcbolt
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Roger -

See the 3D cube HERE

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