whats the need to power them all at once? you could simulate that by just cycling through them faster than the eye can notice. that way you can stay under the large power requirements and not have to have extra hardware to turn them all on at once.
The effect depends on what’s called Persistence of Vision (POV). I came across it when I was looking into building an N x N LED cube. It’s used to create animation effects among other things.
Do a search for POV on youtube. You’ll find lots of projects that use this.
For a start try:
Thanks
I know about POV and shifting them in and out, I just didn’t know how far I could take it.
Here’s the excellent Instructable about shift registers instructables.com/id/LED-mat … /?ALLSTEPS
That’s a good instructable you’ve posted.
2 comments:
1.)
The HEF4794BP shift register can only SINK current, so you can’t just use 4 of them to drive the 8x8 RGB matrix. That’s why a source driver ( UDN2981A ) was used in the instructable to SOURCE current for the LEDs. Also multiplexing was used there, which works fine for just turning the LEDs on and off. The 74HC595 has tri-state outputs (0V, 5V, high resistance), whereas the HEF4794BP has open collector outputs (0V, high resistance).
2.)
If you plan to use PWM to get more than just 7 colors by turning the LEDs on/off “statically”, you should not use the UDN2981 chip! It is far too slow for that and you’ll get “ghost images” on the matrix. Been there, done that. That’s why the Rainbowduino uses a different source driver! It seems to be hard to get though, at least I couldn’t find a place that sells it.
You can see the >> negative smear effect << caused by the UDN2981 chip here at about t = 5s.
Hey Thanks!
Ultimately I would want to do 4 8x8 by 6 8x8. For a total of 32 rows X 48 columns for 1536 dots, each with 3 colors so 4608. Ambitious I know.
I’m just starting off small for now, but will like to build up to the granddaddy. Kinda like my own kind of Peggy.
Thanks again.
The problem here is that the current requirements stay the same if you want the same brightness. When multiplexing, you really need to increase the drive current to the LEDs. For instance, if the LED is only on 25% of the time, you need to raise the peak current by a factor of 4 to achieve the same brightness. The average current will be the same regardless of whether the LED is directly driven, or multiplexed.
The only advantage to multiplexing, is to save output drivers, and to simplify the wiring. For large arrays, multiplexing is the only practical way.
Mike
Hi, i am just experimenting with 2 of these and AS1107 ic’s. Someone was asking what should be the easiest method of controlling these and i found that the AS1107 is just like the MAX7221 plus it handles multiplexing on the chip, so it should be very easy to control a rgb matrix with just 3 of them. And with nice pwm and little controller overhead! I will post my experiments.
Bye