bluetoothLight.h

#include <FastLED.h>
#include <SoftwareSerial.h>

SoftwareSerial mySerial(4, 5); // RX, TX
#define REDPIN   10
#define GREENPIN 11
#define BLUEPIN  9
#define BUTTONPIN 12

const byte numChars = 14;
char SerialHSV[numChars];   // an array to store the received data

boolean newData = false;

int currentHue;
int currentSat;
int currentVal;
int oldHue;
int oldSat;
int oldVal;
int targetHue;
int targetSat;
int targetVal;
int totalSteps;
int currentStep;
boolean bluetooth = true;
int buttonState = 0;
int prevButtonState = 0;

void showAnalogRGB( const CRGB& rgb)
{
  analogWrite(REDPIN,   rgb.r );
  analogWrite(GREENPIN, rgb.g );
  analogWrite(BLUEPIN,  rgb.b );
}

void colorBars()
{
  showAnalogRGB( CRGB::Red );   delay(250);
  showAnalogRGB( CRGB::Green ); delay(250);
  showAnalogRGB( CRGB::Blue );  delay(250);
  showAnalogRGB( CRGB::Black ); delay(250);
}

void recvWithEndMarker() {
    static byte ndx = 0;
    char endMarker = '\n';
    char rc;
    
    while (Serial.available() > 0 && newData == false) {
        rc = Serial.read();

        if (rc != endMarker) {
            SerialHSV[ndx] = rc;
            ndx++;
            if (ndx >= numChars) {
                ndx = numChars - 1;
            }
        }
        else {
            SerialHSV[ndx] = '\0'; // terminate the string
            ndx = 0;
            newData = true;
        }
    }
}
void updateData(){
  if (newData == true) {
    String StringHSV = String(SerialHSV);
      
    if(StringHSV.length() == 13){
      oldHue = currentHue;
      oldSat = currentSat;
      oldVal = currentVal;
      targetHue = StringHSV.substring(0,3).toInt();
      targetSat = StringHSV.substring(3,6).toInt();
      targetVal = StringHSV.substring(6,9).toInt();
      totalSteps = StringHSV.substring(9,14).toInt();
      currentStep = 0;
      Serial.println("New targets: Hue:" + String(targetHue) + " Saturation:" + String(targetSat) + " Value:" + String(targetVal) + " Steps:" + String(totalSteps));
    };
    newData = false;
  }
}
void showColor(){
  if (currentStep != totalSteps + 1){
//    Serial.println("Fadeinput: "+String(oldHue)+", "+String(currentHue)+", "+String(targetHue)+", "+String(currentStep)+", "+String(totalSteps));
    currentHue = fadeStep(oldHue, currentHue, targetHue, currentStep, totalSteps);
    currentSat = fadeStep(oldSat, currentSat, targetSat, currentStep, totalSteps);
    currentVal = fadeStep(oldVal, currentVal, targetVal, currentStep, totalSteps);
    currentStep++;
//    Serial.println(String(currentHue)+", "+String(currentSat)+", "+String(currentVal)+", Step:"+String(currentStep));
    showAnalogRGB( CHSV( currentHue, currentSat, currentVal) );
  }
}

int fadeStep(float oldLevel, int currentLevel, float targetLevel, int currentStep, int totalSteps){
//  Serial.println(String(oldLevel)+", "+String(currentLevel)+", "+String(targetLevel)+", "+String(currentStep)+", "+String(totalSteps));
  float change = (targetLevel-oldLevel) / totalSteps;
  float newLevel = oldLevel + (change * currentStep);
  int newLevelInt = round(newLevel);
  return newLevelInt;
}

void blueFade(){
  for(int x = 0; x < 100; x++){
    showAnalogRGB( CHSV(128,255,x) );
    delay(4);
  }
  for(int x = 99; x < 100 && x > 1; x--){
    showAnalogRGB( CHSV(128,255,x) );
    delay(4);
  }
}

void setup() {
  pinMode(REDPIN,   OUTPUT);
  pinMode(GREENPIN, OUTPUT);
  pinMode(BLUEPIN,  OUTPUT);
  pinMode(BUTTONPIN,  INPUT);
  Serial.begin(9600);
  mySerial.println("Connected via bluetooth to Howard's Light thingy");
  Serial.println("Connected via USB to Howard's Light thingy");
  mySerial.begin(9600);
//  colorBars();
  blueFade();
  showAnalogRGB( CHSV(0,0,0) );
}

void loop() {
  
  if(bluetooth == true){
    recvWithEndMarker();
    updateData();
    showColor();
  }else{
    showAnalogRGB( CRGB(255,80,10) );
  }
  
  buttonState = digitalRead(BUTTONPIN);
  
  if(buttonState != prevButtonState && buttonState == 1){
    if(bluetooth == true){
      bluetooth = false;
      Serial.println("Bluetooth off");
    }else{
      bluetooth = true;
      Serial.println("Bluetooth on");
      blueFade();
      showAnalogRGB( CHSV(0,0,0) );
    }
  }
  prevButtonState = buttonState;
  delay(1);
}