Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: blackbeard on October 03, 2010, 09:23:35 PM

Title: dual 16 channel or quad 8 channel demultiplexer?
Post by: blackbeard on October 03, 2010, 09:23:35 PM

kind of a fuxord thing to look for but i'm trying to find a low chip count solution for my 4x4x4 led cube. can't find one no matter how hard i google. worst case i'll have to go with 2 separate chips which would kind of suck

Title: Re: dual 16 channel or quad 8 channel demultiplexer?
Post by: Soeren on October 03, 2010, 10:52:28 PM

Hi,

A µcontroller is the cheapest and AFAIK only solution to that.

Title: Re: dual 16 channel or quad 8 channel demultiplexer?
Post by: billhowl on October 04, 2010, 12:13:30 AM

you can reduce your pin count quite a bit using charlieplexing.  You can drive n(n-1) segments with charlieplexing.  So a 4x4x4 matrix would require only 9 pins.

http://forums.adafruit.com/viewtopic.php?f=11&t=10661 (http://forums.adafruit.com/viewtopic.php?f=11&t=10661)
an instructable on making a 5x4x4 cube with Charlieplexing:
http://www.instructables.com/id/3D-LED-Charlieplex-Cube-from-Chrismas-Tree-Lights/ (http://www.instructables.com/id/3D-LED-Charlieplex-Cube-from-Chrismas-Tree-Lights/)

Title: Re: dual 16 channel or quad 8 channel demultiplexer?
Post by: madsci1016 on October 04, 2010, 07:57:13 AM

Only problem with charlieplexing is the duty cycle. 64 LEDs = 1/64 duty cycle, or something less if you get fancy, but still bad. LEDS under normal current circumstances can only take about 1/8 to 1/10 duty cycle before brightness drops significantly. To overcome that, most charlieplexing I've seen overdrives the LEDs, and if your code gets stuck, you start blowing pixels. And we are all assuming blackbeard is using single color LEDS. It could be RGB.

Any details of your project blackbeard?