I am attempting to control a single MAX7219 with the LedControl library. I am going to use 60 discrete LEDs (neglecting the remaining 4). Right now I just have 2 hooked up to arbitrary digit and segment pins on the driver. I have tried several configurations with them with the same results.
I first started with my rather large and untested sketch. Instead of only certain (potential) LEDs lighting up, they all lit up (at least the dozen or so I tried). Suspecting my code, I switched to an established demo sketch:
Same result. (I established that this program was running).
The LEDs turn on as soon as I apply power, even before the Arduino begins the program proper. They remain on until I disconnect power. The setLed and related functions have no effect. The shutdown and setIntensity functions don't work either.
I haven't decoupled the power, but it is the only chip off the Arduino and I am using USB power, not AC adapter. Besides, I'm not getting erratic behavior, I'm getting perfectly consistent behavior that just isn't correct! Nevertheless, I will try decoupling after dinner.
I am also considering multiplexing manually. Perhaps there is something I can do with fewer than all the pins, given that I only need to use 2 LEDs at any given time.
Please help? Thanks all!