I've got a long run of some LPD8806 driver-based LED strips (which use an SPI connection) that I am controlling via a Raspberry Pi. It controls it just great, but when I have the LEDs all off (not powered down completely, just having told the driver chips to clear the LED) a few of the lights will eventually turn on. It's really weird, just a few will turn on to random colors after they've been sitting for several hours. Usually 4 or 5 in a row and often somewhere in the middle of the strip.
What I can't figure out is how they are they are getting these random signals. Could it be something with my connection to the SPI pins on the Raspberry Pi? I have the SPI Data out and Clock pins running through a level converter from Adafruit to bring the signal level from 3.3V up to the 5V of the strips.
I'm more of a software guy, so I'm probably just missing something silly. Do the signal lines need some sort of filtering cap maybe?
Update: I've got 2 rolls, 5 meters each, connected in one long run. I am injecting power at the very beginning of the run and where the second roll connects to the first (otherwise the very last pixels were browning out).
What I've noticed now is that it's only ever pixels at the very beginning of the second roll that are turning on. Not sure why, but maybe this will give a clue to what's happening?
I'm up for trying a cap across the power lines... but have no idea what value to use. The highest rated 10uF cap I have on hand is rated for 100V but it's still tiny. Can't imagine that could handle 10A (since I'd have to wire in one cap for each separate power run).