I have an RGB LED strip which I want to control with my arduino uno, everything works fine, except for the green LEDs. They cannot be dimmed to less than 50%, because they will simply turn off.

I have this test code in my setup:

Serial.write("dimming green test started");
for(int x = 255; x > 0; x--) {
    Serial.write(" - g:");
  Serial.write("dimming green test done");

And the green LEDs are fully turned on in the beginning, and at about 127, the just turn off. All the other colors are perfectly dimmable. I checked the energy usage, and green does only use a little more than the other colors, so that's not the problem.

Are green LEDs not dimmable? Or is this just an optical effect?

(I use a setup very similar to this one with one difference: but only use 5V, because my LED strip only needs 5V) setup

  • 1
    switch connections at arduino. swap pin 4 and 7 ... does the problem move to red color?
    – jsotola
    Commented Feb 27, 2018 at 17:43
  • 1
    the pins marked with ~ are the PWM pins ... use those
    – jsotola
    Commented Feb 27, 2018 at 17:48
  • so why does blue and red work :p Commented Feb 27, 2018 at 22:42
  • I used pins 5-7 (so the image was not exactly correct)
    – Finni
    Commented Mar 4, 2018 at 14:06

1 Answer 1


analogWrite only works on pins that support PWM. Those are the pins with the ~ next to it.

On no-PWM pins, analogWrite will set the pin to LOW, for all values lower than 128, and HIGH for all the higher values. Which is what you are experiencing.

  • interestingly, none of the 3 pins chosen by the OP - 2,4 and 7 - have that ~ symbol in the image in the question! Commented Feb 27, 2018 at 22:39
  • @JaromandaX the OP said the image was from a similar project, so I’m not assuming he used those exact pins.
    – Gerben
    Commented Feb 28, 2018 at 12:04
  • with one difference - well, there's three connections to LED's, but only one fails to work ... must be at least two differences between actual wiring and what OP shows in the question :p Commented Feb 28, 2018 at 12:24
  • I used pins 5-7, so only one of them was not PWM
    – Finni
    Commented Mar 4, 2018 at 14:05

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