// Define your PWM pins for the RGB channels
const int redPin   = 0; // Example: PB0
const int greenPin = 1; // Example: PB1
const int bluePin  = 4; // Example: PB4

// The wheel function maps a number (0-255) to an RGB color.
void wheel(uint8_t pos, uint8_t &r, uint8_t &g, uint8_t &b) {
  if (pos < 85) {
    r = pos * 3;         // Increases red from 0 to 255
    g = 255 - pos * 3;   // Decreases green from 255 to 0
    b = 0;
  } else if (pos < 170) {
    pos -= 85;
    r = 255 - pos * 3;   // Decreases red from 255 to 0
    g = 0;
    b = pos * 3;         // Increases blue from 0 to 255
  } else {
    pos -= 170;
    r = 0;
    g = pos * 3;         // Increases green from 0 to 255
    b = 255 - pos * 3;   // Decreases blue from 255 to 0
  }
}

void setup() {
  // Set the RGB pins as outputs.
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);
}

void loop() {
  // Cycle through the 256 positions for a full rainbow cycle.
  for (int i = 0; i < 256; i++) {
    uint8_t r, g, b;
    wheel(i, r, g, b);           // Get the color for this position
    analogWrite(redPin, r);      // Set the red channel
    analogWrite(greenPin, g);    // Set the green channel
    analogWrite(bluePin, b);     // Set the blue channel
    delay(10);                   // Adjust delay for speed of cycle
  }
}