LPD8806 Pixel Anomaly / Power Bleeding (Packaging Issue?)
So... here's something interesting I found. I have a 5m (160-LED) strip of the LPD8806 modules. (Sidebar: these are really cool, and everyone should have some to play with.) I recently noticed the green LED on the very first pixel lights up anytime there is activity on the strip. This didn't become very noticeable until I started running the strip at very high speed.
What it appears to me is that there is some kind of bleeding of power from the clock line into the green RGB pin. The brightness of the green LED is less than the lowest value that you can set using the PWN built in to the LPD8806 chip... but acts as if it being "PWMed" by the clock line. Using the original software library, it is barely noticeable, because the clock is not running very fast (in my tests, around 800Hz). Once I started running the strip faster, the first green LED became brighter.
When I am not updating any LEDs on the strip, the first green LED is not lit. I have confirmed that this is the clock line, because if I upload a very small sketch that pulses pin 13 (SPI SCK), the first green LED lights dimly.
I am just curious to know if anyone else with these strips can duplicate this behaviour. It only happens on the first LED on the strip; none of the others are affected. And, again, it does happen using the original software library, it is just very very dim, and almost unnoticeable.
When I received my reel, the first LED / input side was wound at the center, so I am wondering if this is a result of the strip being curved too tightly when it was wound at the factory... or if it is just a manufacturing defect on that one particular module, which is coincidentally the first one on my strip. I'd certainly hate to declare an entire strip defective over one pixel, but it is annoying that I basically can't turn that pixel off... and at SPI speeds, it is lit very noticeably.
If anyone else can reproduce this issue, I would love to hear about it.