Go Down

Topic: Shiftbrite - Max number of nodes? (Read 1 time) previous topic - next topic

davivid

What sort of limits are we talking about for a single chain connected to an Arduino. Full RGB control at a high refresh rate for smooth transitions.


macegr

Theoretically a 255-module chain could be updated about 700 times per second, but you'd probably run into Arduino CPU limits. Below is an example using OctoBars, which electronically are 8 ShiftBrite controllers, so it's the same as a chain of 128 ShiftBrites. One Arduino had no problem running this chain at 25-30fps and streaming pixel data from a computer over USB.

http://www.youtube.com/watch?v=XZG2opASF0U
Unique RGB LED Modules and Arduino shields: http://www.macetech.com/store

davivid

Great thanks. I love that example - I was thinking of something very similar.

One other thing: is the bus length limited in overall length? or length between each node?

elcojacobs

I just posted I library I wrote to PWM with shift registers. You might want to test it with ShiftBrites.
For 16 brightness levels per LED, you could control 768 LED's at 75Hz
Less LED's --> more brightness levels.

macegr

#4
Jul 19, 2011, 07:49 pm Last Edit: Jul 19, 2011, 07:51 pm by macegr Reason: 1
davivid: Each ShiftBrite is buffered output so the limiting factor is between nodes; we don't recommend more than 2 feet, and suggest the shortest possible cables.

elcojacobs: Your library wouldn't work with ShiftBrites...the ShiftBrite controller already has built-in PWM, 10 bits per color (1024 brightnesses) and 3 colors per module, for 30 bit color, plus a 7 bit current sink fine tuning control per color. However it's good to see normal shift registers stretched to do some PWM as well.
Unique RGB LED Modules and Arduino shields: http://www.macetech.com/store

davivid

macegr: How about multiple chains from a single arduino - say running 3 chains of ~40? or would this cause performance issues?

Also can you suggest a chip to buffer the signal to enable longer cable runs?

Go Up