MAX7219 and 8X8 LED display problem


I’m pretty new to this arduino stuff and am not so hot on the hardware side of things. I wanted to play around with an 8*8 display controlled with a MAX7219. I followed an instructable here.

Now I’ve done everything in the tutorial, but there are clearly some LEDs permenantly on that shouldn’t be. The pic attached is taken with only vcc and gnd connected.

The video here is what happens when everything is connected.

Any ideas what’s wrong?

Looks like your LED matrix is plugged in the wrong way. Unplug it, rotate 180 degrees and plug it back in. If it does not fix the problem then it is something else (maybe the software is not initialising it properly, but you have not provided any software to check).

Hah! I did wonder if it had a "right" way up, but couldn't see any discernible difference between each side. For future reference how can you tell?

Thanks for the tip and providing me with an opportunity to test my un-soldering skills this eve!

So it works? I would recommend using a socket for the matrix :stuck_out_tongue:

Looking at your video again, if this is an eBay type module, the matrix should be on the same side as the IC. This is how they are shown everywhere and soldering it on the opposite side will reverse everything and make it not work.

One side of the matrix has a small square plastic tab that sticks out, as in the photo. On my Parola boards I silk screen the position so that this does not happen.

LED Matrix tab.jpg


Now you really have me puzzled, because it looks like you are using one of the common (eBay) module boards - but you have the chip soldered on one side, and the display on the other.

I am not aware of any board that is intended to be wired that way - from where did you get the board, and which instructions did you use to assemble it?

And what code are you using to test it? What is the pattern supposed to look like? (Post code in "code" - [ # ] icon above the posting window - tags.)

I solved the problem I had with a panel with 5 MAX7219 8x8. I had to edit the library file, MD_MAX72xx_h, and set it to "USE_GENERIC_HW 1" since what comes standard is another.