// RGBLED on ATtiny85
// Reference material: https://www.engineersgarage.com/?s=attiny85

#define rPin 1   // PB1 - Pin 6 - PWM
#define gPin 0   // PB0 - Pin 5 - PWM
#define bPin 4   // PB4 - Pin 3 - PWM
#define vMax 255 // Maximum brightness
#define vMin 0   // Minimum brightness

bool dir;
int rVal, gVal, bVal, i;
float counter = 0;
unsigned long timer, timeout = 10;

void setup() {
  pinMode(rPin, OUTPUT); // configure I/O pin
  pinMode(gPin, OUTPUT); // configure I/O pin
  pinMode(bPin, OUTPUT); // configure I/O pin
}

void loop() {
  crossfade();
  // fadeupdown(); // one color (not blue)
}

void fadeupdown() {
  if (millis() - timer > timeout) {
    timer = millis();
    if (i++ == 255) {
      i = 0;
      dir = !dir;
    }
    if (dir)
      analogWrite(gPin, i);
    else
      analogWrite(gPin, 255 - i);
  }
}

void crossfade() {
  counter = counter + 1;
  rVal = sin(counter / 100 + PI * 0 / 3) * 1000;
  gVal = sin(counter / 100 + PI * 2 / 3) * 1000;
  bVal = sin(counter / 100 + PI * 4 / 3) * 1000;

  rVal = map(rVal, -1000, 1000, 0, 255);
  gVal = map(gVal, -1000, 1000, 0, 255);
  bVal = map(bVal, -1000, 1000, 0, 255);
  analogWrite(rPin, rVal);
  analogWrite(gPin, gVal);
  analogWrite(bPin, bVal);
}

/************************************************************************************************
  ATTINY85                             +-- --+
             PCINT5/-RESET/ADC0/dW/PB5 |1 * 8| VCC
      PCINT3/XTAL1/CLKI/-OC1B/ADC3/PB3 |2   7| PB2/SCK/USCK/SCL/ADC1/T0/INT0/PCINT2
  PWM4/PCINT4/XTAL2/CLKO/OC1B/ADC2/PB4 |3   6| PB1/MISO/DO/AIN1/OC0B/OC1A/PCINT1/PWM1
                                   GND |4   5| PB0/MOSI/DI/SDA/AIN0/OC0A/-OC1A/AREF/PCINT0/PWM0
                                       +-----+
************************************************************************************************/