Creating a charlieplexed LED grid to run on ATTiny85

This instructable was inspired by my first AVR microcontroller project that I've been working on for some time now. I wanted to start learning more about the AVR microcontroller and see how much I could do with the minimum amount of hardware... no extra chips, simple components, etc... just my AVR and my code so I could experiment with a simple set of hardware.

I decided to start with one of the smallest AVRs available, the ATTiny85 with only 8 pins. With only 5 output pins available to me (using 6 would make me lose other chip functionality), I decided to experiment with Charlieplexing. Charlieplexing allows you to control many LEDs with very few output pins, by wiring up an LED in both directions to every possible pair-combination of the pins. In my case, 5 pins would allow control of up to 20 LEDs (5 x (5-1)). This would only require the ATTiny, LEDs, 5 resistors, and a power source.

More info on Charlieplexing:  http://en.wikipedia.org/wiki/Charlieplexing

Step 1 Planning out the wiring

Conceptually, it's not too difficult to understand how to wire up charlieplexing from some of the simpler diagrams available online (see diagram below courtesy of Wikipedia). However, I wanted to arrange 20 LEDs in a tight grid, and managing all the different connections & polarities seemed like it would get complicated as I scaled up from the 2 or 3 pin examples. Most importantly, to avoid mistakes when assembling, I wanted all my LEDs to be aligned the same direction on the board.

In the next step you'll see how the wiring works out for a larger grid of LEDs.

Comments

[taller321led]

HI Please what resistors are necesary for this desing? We simple red leds, 1,6v
Thanks

[devilmaycry]

do the resistors go in beteen the leds??? :( :(

[b2ben]

Not exactly, for each LED, the flow of electricity essentially follows this path:
(Positive Voltage) > (Resistor) > (LED) > (Resistor) > (Ground)

[devilmaycry]

in the very first picture there are only 5 resistors and in the charlieplexed diargram there are 6 Im a bit confused with that .

[b2ben]

All of the diagrams of my circuit have 5 resistors. The Charlieplexing diagram in step two is just an example showing how to charlieplex using 3 resistors and 6 LEDs.

[devilmaycry]

Hi Im currently doing GCSE ELECTRONICS KS4(year10).I really l really love your project and want to make a same on for my GCSE.if u could please tell me what type of microcontroller and the chip will i need to do it.MANY THANKS

[b2ben]

This project was built using the ATTiny85 microcontroller chip

[TieDyedPie]

That's fantastic. You've simplified the wiring, and the implementation in general, nicely.