RGB LED strip inverted PWM

Question

This bug/stupidity-of-myself/problem is killing me:
I'm have created an RGB strip controller that cycles through the additive-rgb-color spectrum while turning a potentiometer.

I have a pot hooked up to my Arduino Nano v3 (from AZ-Delivery, not official Arduino). Then I have an RGB amplifier hooked up to the Arduino with each phase (R, G, B, V+) and to an external power supply (12V by 2A max).

I shortened my program and removed all the value-to-colour-conversion because that has nothing to do with the problem:

void loop() {
    ColorVal = analogRead(pinPot); //read value of color poti
    ColorByte = map(ColorVal, 0, 1023, 0, 255); //Scales 0-1023 to 0-255

    // potvalue to color conversion
    // ...

    // write via PWM to LED
    analogWrite(pinR, R);
    analogWrite(pinG, G);
    analogWrite(pinB, B);
}

My problem: Theoretically you would expect the system to show white when all variables (R, G and B) are set to 255. However, it behaves the other way around. When all values are set to 255 it's off and vice versa. Another example: When R = 255 and G = 0 and B = 0 Green and Blue are lighting and Red is off.

I thought this has to do with polarity or something but I cannot seem to find it out.

Answer 1

The RGB LED strip has a common anode (V+). When you put 12 V on R, G or B, the LEDs have 12 V on both sides, so there is no voltage across it and no current.

And if you put 0 V, they have 12 V across it and light up.

To fix it, just invert the PWM value in your code:

analogWrite(255-pinR, R);
analogWrite(255-pinG, G);
analogWrite(255-pinB, B);