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[on:]

Well I have two MAX7219 boards wired up with leds but I can only sort of get communication with them going.
Also when the leds turn off I hear noise through my speakers and the regulator on the board gets very hot all the time.

When power is applied, all the LEDs are on at full power. The datasheet seems to say that they should be all off.
And when they are 'off' they are only dimmed. Still easily visible though.

With the standard code on the playground (and all the modifications to it that I've done) I can only get all on or all off.
With some code xSmurf used I could get a kind of 'ripple' effect but the effect had nothing to do with what the code was doing although the timing was right (delays stopped the ripple).

I'm kind of out of ideas. They are behaving rather weirdly.

[Reply #1 on:]

hi cheater,
you probably just connected the leds the wrong way!?

[Reply #2 on:]

Would that cause the symptoms I'm seeing?
I thought that would have just inverted the display. :-?

[Reply #3 on:]

i'm not sure about all symptoms (speaker noise) but as far as i can tell, you cannot simply reverse the LEDs to invert the display. the led matrix won't work the other way around. at least not with the max chip, which i think PWMs the rows and columns.
i'm not toooo sure here, so before you're going to desolder 64 Leds, maybe try it with another chip first.

kuk

[Reply #4 on:]

Oh you've misread my first post. The stakes are much higher.
We arent talking about 64 leds. We are talking about 128 leds. :'(

I just checked by putting a led on another's leads but reversed and unfortunately it appears to be working.
Will someone please come up with a better reason why its not working so I dont have to desolder that many LEDs?

[Reply #5 on:]

aww man, u gotta desolder over 200 pins?

that blows, i feel for you. Good luck, and just do it, don't think about it...

[Reply #6 on:]

cann't you just invert the code, so when the led should be on, you write them to low,....
just a short idea, with out any real thinking ,...ahhmmm...

anyway
tomek

[Reply #7 on:]

cann't you just invert the code, so when the led should be on, you write them to low,....
just a short idea, with out any real thinking ,...ahhmmm...

Thats what I was thinking but apparently not.

[Reply #8 on:]

Hi,

...
I just checked by putting a led on another's leads but reversed and unfortunately it appears to be working.

I came across the problem you reported a few times now. I had no idea what could be the reason for this strange effects.
It still doesn't make sense to me that LEDs which are wired the wrong way light up at all, but well ... you proved it!??
I' going tol build a small "Not-working-inverted matrix" over the weekend and see if I can make sense of the whole thing.

You probably solved some "MAX7219 Mysterious Light-Effects" postings, because you are the first one coming up with an explanation for the problem.

Will someone please come up with a better reason why its not working so I dont have to desolder that many LEDs?

If the LEDs are on a PCB, you are probably out of luck. But if you build something like this (which would be the correct wiring for the LEDs) with wires that run from the matrix to the MAX7219

and you inverted every LED on the matrix, you can swap all the segment- and digit-connections and end up with a correct matrix.
You have to wire :
Dig0 on your matrix to the SegDP-connector of the MAX7219 and SegDP from your matrix to Dig0 on the MAX7219.
Dig1 on your matrix to the SegA-connector of the MAX7219 and SegA from your matrix to Dig1 on the MAX7219.
and so on...

That should do the trick
Eberhard

[Reply #9 on:]

It still doesn't make sense to me that LEDs which are wired the wrong way light up at all, but well ... you proved it!??

Its because its HIGH and LOW not on and off.
When wired up incorrectly, it just happens to light up with the correct polarity when its trying to light up another led.

You probably solved some "MAX7219 Mysterious Light-Effects" postings, because you are the first one coming up with an explanation for the problem.

Oh wonderful. I'm still busy procrastinating about those 128 leds I need to desolder.
They are on a custom pcb of course so its not simple.

[Reply #10 on:]

Wayoda wrote

I'm going to build a small "Not-working-inverted matrix" over the weekend and see if I can make sense of the whole thing.

I did, but couldn't replicate the "weird blinking" problem. Probably because I use only MAX7221.
With these chips all LEDs stay dark, no matter which command is send to them.
This "weird blinking"-debugger is a true advantage of a MAX7219.

@cheater
Did you solve your problem yet. If everything works fine with your LEDs in correct polarity, I would add a troubleshooting  section to the playground article http://www.arduino.cc/playground/Main/MAX72XXHardware

Eberhard