Problem wiring an Uno v3, MAX7219 and an 8x8 matrix.

I getting to my wits end. I am using this reference for the MAX7219.[1] and this to show the hookups from the chip to the matrix*[2]* . I am using an uno v3 and the matrix is from adafruit. It is the mini 8x8. This is the pdf*[3]* for the matrix. I am also using the led control library. gif of what I get. [4] I guess I can't seem to read the 8x8 schmatic or I am just doing it all wrong. I can't count how many time I have pulled all the jumpers and tried it all again.

Here is my latest try. I only put a few wires in and I tried to copy the wires from another video showing one wired up. Here is a video of the of this setup.

I know there are rows and columns and I can see what wires go to the MAX7219 but to the matrix I am confused.

Any help would be great. Thanks! Andy

[1] [2] [3] [4]

Your video is private.

The most common error is the matrix plugged in the wrong way around/upside down. Have you tried reversing that?

Andy, your pic of the breadboard looks like spaghetti, but I may have spotted something - the Gnd rail at the top of the breadboard. I can see the two Gnd pins on the '7219 are connected to it, but I can't see any other connections. Should you have put another jumper in to connect it to the other Gnd rail at the bottom of the breadboard?

Also, so we are 100% clear, is your matrix the AVB (=common Anodes on rows) or the CVB (=common Cathodes on rows) variant?

One reassuring thing I can also see from that pic. Looks like you have a genuine Maxim chip rather than one of the very common fakes usually sold on eBay. The dimple by pin 1 is how you tell. I guess you paid $10 for it rather than $2!


marco_c: Your video is private.

Sorry about that. Video is now public. The video show what is happening now. It looks like things are working but I do not know what wires go where. If I could figure that out I'd be good.

PaulRB: Also, so we are 100% clear, is your matrix the AVB (=common Anodes on rows) or the CVB (=common Cathodes on rows) variant?

The .pdf for the matrix says it is Row Cathode which I'm guessing is common cathode.

Also I have a jumper just out of the pic that connects power and ground to the other rails. I did buy the MAX7219 from adafruit and piad $10 for it. :)

Thanks for taking some time to help out.

andyfriedl: The .pdf for the matrix says it is Row Cathode which I'm guessing is common cathode.

Well, the term "common cathode" is useless when describing led matrices. They are all common cathode. And the are all common anode too. The two different possible configurations are common cathodes on each row and common anodes on each column, or vice versa. Even then, with a square matrix, who is to say which way up it should be held? Turn it 90° and rows become columns. The convention is that the two rows of pins on the back are horizontal rows.

The data sheet describes both types, so what is printed on the matrix itself?

Max7219 was originally designed to drive up to 8 digits of 7-segment led display. It can only be used with common cathode 7-seg displays. Those have 8 pins for each of the individual leds in the segments, and one common pin for the common cathodes of each digit. The max7219 can drive either type of 8x8 matrix because, as I said, all matrices are common cathode.

So all you need to do to get the wiring right is make sure the cathodes in your matrix are connected to the DIGit pins on the chip, and your anodes are connected to the SEGment pins on the chip. Then it will work.

HOWEVER if you are going to be using someone else's sketch, you have to wire it up exactly as they did, otherwise the shapes/symbols displayed will be upside down, mirror image, or just garbled. If they had row anode and you have row cathode, the symbols will be rotaded by 90°.

Does that help?

Seriously, thank you for helping me learn what is going on here. Your reply does help. My matrix is the KWM-20881CUGB.

I am confused by the schematic that shows the matrix. What are the circled numbers and how do they relate to the matrix? Do the circled numbers relate to the pins on the matrix?

Thanks :)

So its an equivalent product to the one in your data sheet from before. The data sheet looks practically identical and the “C” in the code indicates cathodes on rows:

The wierd thing is that data sheet describes them as “yellow green” but yours is obviously red…

You are correct about the circled numbers.

So, I think I am done for a while. I hooked it up using all the info I have. I found this. and this is what I got. ............ Is it possible I blew or messed up the MAX7219? It is like I am screwing something basic up. I need to step back from this. It seem like all the advice is consistent and somehow does not apply to what I am doing. I am going to strip it all down and start over... Don't know what else to do.

Thanks for the help