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Topic: Understanding the components of a LED matrix (Read 1 time) previous topic - next topic

dhenry

At 20ma/pin, it will outlast all of us, by a few multiples.

M4573R


At 20ma/pin, it will outlast all of us, by a few multiples.



To be clear, we're talking 20mA per pin on all 8 pins at once, double the chips rated current. If that's true, I could use the 595's and a 2083 to even extend this to a 4x4x4 or 8x8x8!

dhenry

Quote
If that's true,


You can easily try it.

M4573R


Quote
If that's true,

You can easily try it.


I can try a lot of things! But I'd like to save my wallet from burning through chips and my mind by saving hours of debugging related to things like this.

Hippynerd

Since you are talking about an 8x8 multiplex, thats a total of 16 control lines, you can do that with just resistors and LEDs, multiplexing is good enough.

If you want to reduce your control lines you can do that by serializing the data, but with this size you are not saving a lot, unless you serialize both at the same time (16 pins to 3 pins, vs 16 pins to 6 pins). It seems like you should be able to use 2 shift registers (one for source, one for sink).

Since you will only have 1 row on at a time, you have a 12% Duty cycle, so they may not be as bright as if you just have them on. If you want them as bright as each one can be, then you could serialize all the anodes or cathodes to 64 pins through 8 shift registers and 64 resistors. You can then have 100% duty cycle.

If you wanted do 100% duty cycle, but didnt want to do the resistors, you could use constant current drivers, heck, you may even be able to find a single chip to solve that.

The ShiftPWM demo runs 3 shift registers to 24 resistors to 8 RGB LEDs (thats 3 diodes per LED). Its sinking or sourcing up to 480mA through 3 70mA devices.  So, in theory, it could source or sink 480 through something rated for 210 or about 225% of its rating. I personally have only run it for a few days, but I had no problems, It theoretically could be doing damage, but I dont know how long it takes to fail, days, weeks, years, its hard to say.

The charliecubes I have running over a month are pretty crazy, thats 192 LEDs running on an arduino, with no other parts. Its just crazy, thats almost 4 amps if the leds were fully driven at 20mA each (64 RGB LEDs = 192 LEDs @ 20mA each= 3840. This all runs from a single arduino, on a 500mA usb power supply, so there is no way its using 3840mA.

here are some things that I have tried:
https://www.youtube.com/watch?v=CD-6Dq9qV9s
https://www.youtube.com/watch?v=53SB525n2QY
https://www.youtube.com/watch?v=ZN0qXgcU-w0

What have you tried?

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