Hello AAC forum,

Work on controlling about 300 LEDs using an Arduino Uno and the Maxim7219
multiplexer.
Designing a PCB to cascade five 7219 ICs.

There is a lot of info on using these ICs with either a matrix or a seven-segment LED
at the Arduino playground, tronixstuff article, /brainy-bits.com and several others.

This display is 300 LEDs in a curvilinear line.

This schematic is from the Arduino playground

is altered to produce

This design has been bread boarded and proven.
Now a PCB is contemplated.

Besides a general review of the board before I blow two day's pay on getting five of these knocked out, a question is requested.
In some of the designs reviewed a 200 ohm resistor is placed in serial between the IC cathode pins
(pins 2, 3, 5, 6, 7, 8, 10, and 11) and the LED headers to control the source. In fact, when the 7219 was cascaded it was noticed that the LEDs controlled by the second IC were noticeably dimmer than the LEDs connected to the first IC. Perhaps it would be smart to put a trim pot in the cathode traces so the brightness of the LEDs could be controlled from IC to IC.
Have looked at trim pots by Bourns and Murata at Mouser and Digikey. But the only trim pot found in the 200 ohm range goes from 100 ohms to 1 megaohm. Quite a range. It was surmised that a variable resistor in the 100 to 1000 ohm domain would be best. Does one exist?
Thanks.

Allen Pitts, Dallas Texas

 

These are 220Ω and 470Ω trimmer resistors from Mouser.
https://www.mouser.co.uk/Passive-Co...tors-Through-Hole/_/N-9q0yt?P=1z0x8beZ1z0x8b3

 

You may want to consider a cheaper alternative, like here. https://www.amazon.com/dp/B00LSG54O...t=&hvlocphy=9007812&hvtargid=pla-314726048848

Six of these would be less than $40 and you would get 6 X 8 x 8 LED matrices for another project down the line. Even if your particular design requires individual LEDs, your board is breaking out the rows and columns to 8 connection points each - which could also be done elsewhere.

The same functionality as your board looks like it can be purchased here for $13 (including MAX7219 and other components). That's $65 and all you need to add are the LEDs.

Just some thoughts.

 

I agree with raymond, take a look at those modules.

If you are dead set on making your own PCB, your "two days pay" comment leads me to think you might not know about places like Seeed, OSHPark and pcbway. Of course if you only earn, $20-40 a day, never mind.