# 11x42 LED Matrix with Arduino UNO

Discussion in 'Microcontrollers, Programming and IoT' started by leonardw94, Oct 18, 2015.

1. ### leonardw94

3
0
Oct 18, 2015
Hey Forum,
I'm planning to build an 11x42 LED Matrix for my Daft Punk Helmet .

I decided to split into 2 sub-matrizes, 11x21 each.
Therefore I will need 11+21 = 32 bits to control each sub-matrix with multiplexing.
I thought of controlling the matrix with a 32-bit shift register.

The shift registers will be driven an Arduino UNO that also provides the 5V current.

The rows will be the cathodes, the columns will be the anodes.
I want to scan it row by row, so that every row is on 1/11 of the time.

Now, here's my problem: The number of leds that are lit in one row varies between 0 and 21 obviously. That means the resistance needed varies a lot, too.
How do make this work and assure all the LED have the same brightness (and don't fry, obviously)?

I've read about some things people used for their matrix, but I don't know which one really solves the problem:

-MAX7219 LED driver
-Current Driver/ Current Sink
-Transistors/FETs
-Darlington Arrays

Also, how do I deal with the odd numbers (11 and 21)? Most of the drivers come in 8 / 16 / 32 bit only.

Thanks for helping!

2. ### Colin Mitchell

1,417
313
Aug 31, 2014
One of the drive lines has only one LED on at a time or no LED. That's the line you put the resistor.
9% of the time is not going to give very much brightness and you will need sinking transistors.
You are much better off the have a run of 5 and a run of 6

3
0
Oct 18, 2015