LED matrix power control

Using Arduino LEDs and Multiplexing
#1

Hi all

I'm working on a project that is to make myself a keyboard.

Basically, the idea is a 4x16 key switch matrix with a 4x16 LED matrix.

I just want to have every single LED under control with PWN, so I work with a 328p driving TLC5940 and p-MOS and the sampling testing is pretty good.
So I'm thinking if I can make the matrix RGB and here's the problem.

my current limiting is set at 20ma, for a 4x16 matrix it's at 20x16=320ma which is pretty safe for the USB port.
But, if I make it RGB, it's like 3x20x16=960ma and it's go boom.
Of course, it happens only when all 16 ports at 100% duty and you push 16 buttons at the same time which I can say almost impossible; but I'm wondering if there's a way that I can control the matrix's peak consumption at like 450ma?

I have a 500ma fuse but I don't want it just reset that often.

Thanks

#2

Option 1, don't turn them all to full brightness in software

Or option 2, and I think a more reasonable option, limit the current to 5mA or so. 20mA through a modern led is A HECK of a light! I would say wayyyy to bright to use in a keyboard anyway.

#3

But, if I make it RGB, it's like 3x20x16=960ma and it's go boom.

Not boom but sag.

Yes more LEDs mean more current. It's Physics, you can save current at the expense of brightness by multiplexing them so that only say 8 are on at any one time.

It sounds like you are basically making an RGB monome. Here are two I made earlier.
http://www.thebox.myzen.co.uk/Hardware/Mini_Monome.html

http://www.thebox.myzen.co.uk/Hardware/Hexome.html

#4