MAX7219 Anode / Cathode question

Other Hardware LEDs and Multiplexing
1

Working with the R2 builder group on revising a few PCB boards for R2 lights.
These use 3 MAX7219 ICs to control #137 3MM LEDs.

Now the original PCB design didn't have a ground plane, so there was a lot of wasted real estate in creating ground traces on the PCB. I've since then removed all grounds and added a new ground plane, but I'm left wondering about the LED cathodes and if I can clean them up too.

I can see that the MAX7219 has large arrays of LEDS hooked up to SEGXX across the ICs and the cathodes hooked up to DIGXX across the same array.

So my question is, what happens if I disconnect cathodes from DIGXX of IC's and tie them to my new ground plane? Will the IC / LEDs still function as intended, or is digital pins on IC not acting as a ground, but much more?

I ask this without having the actual parts in hand; other wise I would of tested prior to post.

Thank you!

2

I think it is - or should be - fairly obvious that if you do not connect the LED cathodes to the MAX7219. that you will not be able to control the LEDs with the MAX7219, which is after all, the purpose of using a MAX7219. :astonished:

The same would necessarily apply to connecting the anodes to Vcc instead of the MAX7219.

Seems you have a bit to learn yet about engineering if not electricity and electronics. :grinning:

3

MAX7219 works by driving current out on 8 pins to 8 LED anodes, and sinking current from one cathode.
Then repeating: 8 anodes, 2nd cathode.
8 anodes, 3rd cathode.
There is no Gnd plane connection.
See KWM-30881CVB here

That is how multiplexing works.
If you connect the LEDs to Gnd, the multiplexing will not work and you will damage the MAX7219.