This may be a dumb question but I have a two colour 8x8 LED Matrix with a total of 24 pins on it. All of the pins need to be connected to the Arduino in order to be controlled, but the Arduino does not have nearly enough pins on it. So my question is how do I control the array with one Arduino?
You need some extra hardware. Is it common anode or common cathode?
The answer is led multiplexing, search it ("led multiplexing arduino")...lots how resources available.
There is this driver board but i think your matrix must be common cathode to be compatible.
I have looked over a large number of multiplexing articles/examples and I have to admit that I am rather confused (I may be in over my head). In any event I want to push forward to see if I can figure this out but I am a little stumped at to where I should start in terms of hardware. The LED Matrix that I have is GMA26881C bi-coloured (here is the data sheet for what it is worth: http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/GMA26881C.pdf) and I do not really know what to use to multiplex. I think that a shift register might be easiest??? Although ultimately I would like to control multiple Matrix's and I think I might still be stuck with not having enough pins??? So yeah, I guess my question is what hardware would people recommend I use?
Thanks for the help.
With discrete shift registers and current limit resistors, your sketch has to do all the multiplexing.
Using a part like the Holtek in reply #3, your sketch just puts data into shift registers in the chip, and the chip does all the multiplexing for you. Much easier to add more displays, while doing your own multiplexing just adds to the processing the Arduino has to do and cuts down on brightness and reduces the achievable refresh/update rate.
Reading that data sheet, i am confused. The very first thing it says on page 1 is common cathode. But later pages show it has 8 anode pins and 16 cathode pins. I would describe that as common anode.
So I'm not sure if the ht1632 board is suitable or not...
Board is marked with 16 As and 8 Cs.
Page 37 also shows a 16-anode/8 cathode set up.
http://www.holtek.com/english/docum/consumer/16K33.htm
Alright, so it seems that I might have hit another snag. The matrix that I am using seems to have been discontinued. The reason that this is an issue is because I want to buy a class set for my students. So now that I need to look at an original project I was wondering what peoples thoughts were on if I should try to get another 2 colour display, or if I should just keep it simple a go with a one colour display? Or do I just go full out and get RGB displays?
The intended projects that I am working towards are simple games like pong.
Obviously, single colour displays will be cheapest. You can buy 8x8 matrix and max7219 boards on eBay for peanuts.
){kind=link}
8x8 rgb matrix is easy if you get the ws2812 variety. No controller chip needed because each led contains its own controller. However, current could be an issue. 64 ws2812 leds could draw up to almost 4A, way too much for Arduino's on-board regulator.
CrossRoads:
You need some extra hardware. Is it common anode or common cathode?
I have never understood how that terminology makes sense for a LED matrix.
I guess I could understand "column anode" or "column cathode".
Datasheets typically use
- Row Cathode Column Anode
- Row Anode Column Cathode
And even then it typically is only a reference to how the pins are oriented and either can be made to work if hooking up your own wires.
--- bill
bperrybap:
I have never understood how that terminology makes sense for a LED matrix.
It doesn't, of course.
Unless it is a multi-colour matrix.
Paul__B:
Unless it is a multi-colour matrix.
touché 
For dual LED matrix, common anode & common cathode make sense. Look at the original datasheet presented - 2 sets of anodes, 1 set of cathodes in common for 16 LEDs.
For single LED, column anode/column cathode, sure, can turn the same display 90 degrees & use for either.