I created an LED “thermometer” using the FastLED library and TM1803 LEDs (http://www.instructables.com/id/Arduino-LED-Strip-Thermometer/).
It was quite cool in my office this morning, so I noticed that when the LEDs are “off” (set to black), that they still glow a slight green.
So, using the statement: leds[4] = CRGB::Black; as an example, doesn’t turn the LED segment off.
Thoughts?
http://www.instructables.com/id/Arduino-LED-Strip-Thermometer
Just curious: what microcontroller are you using, and what version of FastLED? 3.1?
I experienced something a tiny bit like this with some LPD8806 strips with the first pixel in each of my 4 segments ever so slightly glowing green when off. I found that adding a 2ms delay to my main loop fixed it.
Marc: that’s interesting. I wonder if we need that in the library itself.
In my case with the LPD8806 strips I think it was the clock line signal bleeding over to the data line. I believe it’s more of a hardware then software problem. And the first pixel glowing green was only apparent when looping really fast (and thus calling show very often). Hence the delay, even just 2ms long in my case, seemed to fix it.
Here’s a post I ran across in the Adafruit forums about this with the LPD8806 strips.
http://forums.adafruit.com/viewtopic.php?f=47&p=121660
Thanks. Useful to know and share.
@Mark_Kriegsman I’m using an Arduino Uno R3 and FastLED 3.1
@marmil I have a 30 delay between each show call.
You’re probably right though… if I upload a sketch that only shows (showColor(CRGB::Black)) and loop through, the “green pixels” randomly jump around.
I’m curious if making that 30ms longer (or shorter) affects the flicker at all.
(Also: that video is private at the moment; I can’t see it)
My bad… it’s a 30 second delay.
I’m noticing something that may be related… it seems the more of the strip that is lit, the less it happens. For example… right now, all segments but the last two are lit and there are no “black is green” leds.
I also made the video public.
Ah ok I see the video now. Huh. Just curious, what’s the RGB order for this strip? GRB?
Ok thanks. I’ll try to see if anything looks quirky in the library code; please let me know if you get any new data from the actual rig.
Curious, when you run the RGB Calibrate sketch are the pixels after the RGB black or do they have the green glow?
Other ideas popping around in my mind after watching the video… the way things are jumping around made me wonder if it’s power related.
Did you confirm the voltage you’re getting at the beginning of your strip?
What about adding a capacitor across the power terminals of the strip and a resistor to the data line?
@marmil They are all black, other than the first 6 segments (obviously).
What happens if you upgrade to arduino 1.6.5?
I’m running 1.7.5 of the IDE.
Oddly, the problem seems to have gone away today. I have done nothing other than the tests. I wonder if something was “stuck” in the LED’s chipset and has somehow become un-stuck?
For the record, I used to run a tech support division of a national software company and have always hated “it just started working” answers. lol
Well, if there’s one thing I’ve learned in the Arduino world it’s this: all abstractions are leaky. We think of software as deterministic, but between power glitches and memory overruns, it isn’t. We think of “digital” hardware as have discrete states, but between mismatched grounds, 5v supplies putting out 5.3v, capacitive effects of long wires, RF crosstalk, and loose connectors,we’re often forced to look down the abstraction stack-- sometimes way down. (Yesterday I had an LED strip that I’d wired up that just wouldn’t work… Turns out that one of the wires that I’d used was bad inside.)
Anyway, glad it’s working today. May it still be working tomorrow!
I really appreciate the effort!
Well… the “black is green” is back again today.
It’s nice and cool in the office this morning, so only 6-7 of the 10 segments are lit. The remaining three should be “black” but have the green thing happening.
Seems like when less segments are lit, current may be bleeding over? I’m no electronics expert, but would a resistor or capacitor make a difference?