max7219 woes

Hi folks,

I've started work on a friend's LED display and chose the max7219 because of the readily available library and seemingly ease of use. I've kind of hit a brick wall and i'm not sure what exactly is going on.

When i run the simple led test sketch included with Arduino011 in the Matrix library examples, one row goes completely blank, and 11 different LEDs turn on and off intermittently. I shut down and rebooted and then got the whole matrix lit up, with a very dim flashing on a handful of lights. I have a matrix.clear() message, so in the least every two seconds the whole thing should turn off. When i do a simple sketch just telling the matrix to be cleared, no leds are switched off. When i have a simple sketch of just turning on and off a single led, generally nothing happens.

To the best of what I can tell, we have wired up the matrix in just the way that the schematic indicates, and we have checked and rechecked the wiring to make sure we got it right.

one thing I can think of is that RSet (the sole resistor) is not the correct value. Would this affect the matrix in the above way or just give too much or too little current to all of them?

Also, the wires to the max7219 from the matrix are rather long. The display itself is about 5ft x 4ft, so there is a lot of wire between them all and the ic. would long wires contribute to this strange behavior?

If anyone has any thoughts about what might be causing this irregular, please let me know. We are in a bit of a time crunch!

Also, i can probably whip something up using SimpleMessageSystem, but has anyone ever controlled one of these with Max/MSP and want to share a sketch?

I use about 26K for RSet.

The display itself is about 5ft x 4ft, . . .

Is the display something you created yourself? It's common cathode, right?

yea, its something we put together ourselves, using the schematics that are on the max27xx page:

when i look at the diagram, i’m assuming that the Digx pins get the positive (the bottom of the triangle is +), but is that completely backwards?

i'm thinking we wired it completely backwards now...ack. common cathode would mean that the negative terminals all go in series to Digx, yea?

thanks for any help that you can provide!

-b

common cathode would mean that the negative terminals all go in series to Digx, yea?

Yea, I’m afraid that’s right. :frowning:

(I am anodely and cathodely impaired, so double check my advice.)

I have read some posts about some people trying / getting (?) a common anode to work with the MAX72xx using transistors or an inverter, but I don’t know enough to give you advise on that.

There is also useful info in the Playground . . .
http://www.arduino.cc/playground/Main/LEDMatrix

Good luck :sunglasses:

yep, that was it! oof, live and learn!

again, if anyone has used SimpleMessageSystem in conjunction with the Matrix library, i'd love to see a sketch!

thanks for the help so far!

-b