Hi board,
I've been trying to follow the various tutorials online about getting the max7219 and arduino interfaced, but no matter what I do, I can't seem to get anything besides 64 lit LEDs. I'm assuming this is some sort of debug mode for the 7219, but I can't seem to get it out?
Do you guys have any tips? Thanks!
More likely you have a wiring problem.
Are you using a commercial prepackaged LED matrix (i.e. not using a matrix that you made up of individual LEDs yourself)?
Commercial matricies often have there own wierd pinouts - double check the datasheet for your LED matrix and make sure you have got the row/columns correct.
As far as I know there is no "debug" mode on the max7219, mine defaults to "all off"
I soldered my own matrix. I can verify that most of the LEDs are working (there are a few that seem to have burnt out while soldering).
Would this be caused by not having the correct capacitor bridging +5V and GND? I've been running without a cap because I don't have any usable electrolytics...
No, I don't think the lack of the capacitor would cause the problem you are seeing. Along with general filtering, the capacitor would be used to supply some power when the max7219 causes a dip on the supply line by suddenly turning all on.
Nice work on doing your own matrix. Seeing as how yours are are all on, and the default is all off, is it possible you have the matrix wired up as a row anode and you think it is column anode (or vice versa)? As a check, you could swap all the connections i.e. row 0 to column 0, row 1 to column 1 etc...
I tried swapping the row/column connections, but then no LEDs light.
The only thing I can think of is that the few LEDs that are out are screwing up the 7219 some how. I'm thinking about re-doing my matrix right now...
I might try swapping the connections again to see what happens. Maybe I didn't let the software light up any of the LEDs...
(Thanks for your help, by the way)
So when you get to the stage that none of them light, are you confident you are sending the proper commands to the max7219? What libraries are you using?
might be worth using a commercial matrix to do some testing, then moving onto your own matrix when you know you've got the software side working. at least that way troubleshooting is a bit easier. that's what I did with my LED matrix coffee table (shameless plug...)
I've tried the code here:
http://www.arduino.cc/playground/LEDMatrix/Max7219
and the library that is included in the arduino IDE examples.
Which have you used?
I'd definately try wayoda's "LEDcontrol" library -
http://www.wayoda.org/arduino/ledcontrol/index.html
I got my matricies working using LEDControl, but to be fair I was still making newbie hardware mistakes when trying to use the "matrix" and "sprite" libraries.
It looks like the LEDcontrol library is built for SPI, when the 7219 is not fully SPI compatible. Did you use LEDcontrol with a 7219 or a 7221?
Fixed it: the problem was (as you suggested) that I had the anode/cathodes swapped. After using LEDcontrol and getting the polarity correct, all is well.
Minus the 11 bum LEDs...
Thanks!
Nice!
Sorry to resurrect my old thread, but this issue is cropping up again, but with a different LED array.
To replace my self-made LED array that I burnt out, I purchased some of these: ebay link
I am fairly certain that the pinout is either exactly or similar to this pinout link since I tested a bunch of the lead combinations with a battery.
...but when I hook it up to the MAX7219, the array lights very inconsistently. When 7219 enables an LED, it lights with full brightness, but when it turns it off, the LED stays lit but is not as bright.
When I try to reverse the polarity (like the problem I had with my home-made array), the LEDs don't light at all, so I'm fairly certain the polarity is correct.