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View Full Version : Fun with cross-talk / inductance! :)



tetsuo
12-16-2013, 06:41 PM
A fun illustration of inductance in action! The 16 rows of LEDs seen here are actually 4 "strips" of WS2812b LEDs. During testing a few days ago, the data lines got pulled out of the breadboard. When i plugged the first one back in, I noticed that 3 of the 4 strips started updating. Not only that, but they worked beautifully! Testing w/ the scope showed a reasonably good-looking signal on two of the completely disconnected strips, and a fairly noisy one on the third. The funny thing is, the WS2812b reshaping kicked in for the first two and sent a nice clean signal down those strips.

TL;DR - in this video, only 1/4 of the leds are connected, but 3/4 of them are updating :)

http://www.youtube.com/watch?v=3Rc1hiCo878

Simply grounding the other channels rather than leaving them "floating" immediately halted the behavior... I still dont quite get that! I expected to still see some amount amount of cross-talk on the scope, but it showed a relatively noise-free 0V.