Blue LED addressing problem
I purchased a set of 160 digitally addressable LEDs a few weeks ago (the kind with the LPD8806 chip) and there seems to be a software glitch in the Arduino library. I cut the strips into 10 strips to make a 16 x 10 matrix for a holiday sign. I've glued the 10 strips to a wood backing, then soldered them back together. Each 16 LED strip has it's own power wires, connected together on the back of the sign with screw terminals. I also bought a proper ATX 2.2 12x2 connector to power the sign with a computer PSU, but it isn't wired yet and I wanted to do some simple testing to make sure the sign works ok, so its all powered off the Arduino which is running the long strand test. (The test that only powers one LED at a time.)
The problem I've run across is that the second last LED in the strand (LED 158) is yellow when its supposed to be white while running the test. (The blue LED isn't lighting.) If I modify the code so it thinks its addressing 180 LEDs instead of 160, it all works fine. I've tried writing a simple sketch to light just that LED, with the library set to 160 LEDs, and I get the same problem.
The wrong color is always the same (not lighting the blue LED) and its always on that particular LED. During the test of individual red, green and blue channels the LED works fine.
The fact that things work fine if I set the library to address 180 LEDs suggests that this is a software problem. (I really hope its a software problem because I'd hate to have to remove the strip from the sign.)
I'm using an Arduino Mega 2560 with nothing but the library and the simple long strand test program, so this shouldn't be a memory issue. By the looks of it, the library would be using 494 bytes of SRAM with 160 LEDs which, even accounting for C++ and Arduino library overhead is nowhere near the 8K limit of the Mega.