photocellDecodeMorse.ino

#define SIZE 26

// See demo in https://youtu.be/vD1pToPe5N4 

String letters[SIZE]={
// A to I
".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", "..",
// J to R 
".---", "-.-", ".-..", "--", "-.", "---", ".--.", "--.-", ".-.",
// S to Z
"...", "-", "..-", "...-", ".--", "-..-", "-.--", "--.." 
};

int photocellPin = 0;     // the cell and 10K pulldown are connected to a0
int minToBeHigh;
int maxToBeLow;
unsigned long DOT_MIN_LEN = 100;
unsigned long DOT_MAX_LEN = 200;
unsigned long DASH_MIN_LEN = 500;
unsigned long MIN_TIME_BETWEEN_LETTERS = 700;
unsigned long MIN_TIME_BETWEEN_WORDS = 5000;

String lastStatus = "OFF";
String statusNow;
unsigned long lastChangeTime;
String lastSignsInLetter = "";

void setup(void) {
  Serial.begin(9600);
  
  // calibrate - read 50 times = 10 measures * 5 sec
  int measuredLow = 9999;
  int measuredHigh = 0;
  for (int i=0; i<50 ; i++) {
    int measured = analogRead(photocellPin);
    print("measured = "); println(measured);
    if (measured > measuredHigh)
      measuredHigh = measured;
    if (measured < measuredLow)
      measuredLow = measured;
    delay(100);
  }
  print("measuredHigh = "); println(measuredHigh);
  print("measuredLow  = "); println(measuredLow);
  int epsilon = (measuredHigh - measuredLow) / 10;
  print("epsilon      = "); println(epsilon);
  int avg = (measuredHigh + measuredLow) / 2;
  minToBeHigh = avg + epsilon;
  maxToBeLow  = avg - epsilon;
  print("minToBeHigh  = "); println(minToBeHigh);
  print("maxToBeLow   = "); println(maxToBeLow);

  lastChangeTime = millis();
}

void loop(void) {
  unsigned long timeSinceLastChange = millis() - lastChangeTime;
  //print("timeSinceLastChange = "); println(timeSinceLastChange);
  
  //delay(10);
  int measured = analogRead(photocellPin);
  //print("measured = "); println(measured);
  if (measured > minToBeHigh) {
    statusNow = "ON";
  } else if (measured < maxToBeLow) {
    statusNow = "OFF";
  } else {
    //println("measured as avg");
    return;
  }
    
  if (statusNow == lastStatus) {
      return;
  }

  // there was a change in the light
  //print("there was a change to "); println(statusNow);
  //print("from "); println(lastStatus);
  lastStatus = statusNow;
    
  if (statusNow == "OFF") {
    if (timeSinceLastChange > DOT_MIN_LEN && timeSinceLastChange < DOT_MAX_LEN) {
      lastSignsInLetter = lastSignsInLetter + ".";
      //print("timeSinceLastChange = "); println(timeSinceLastChange);
      println("lastSign     .");
    }

    if (timeSinceLastChange > DASH_MIN_LEN) {
      lastSignsInLetter = lastSignsInLetter + "-";
      //print("timeSinceLastChange = "); println(timeSinceLastChange);
      println("lastSign     -");
    }
  }

  if (statusNow == "ON") {
    // new letter
    if (timeSinceLastChange > MIN_TIME_BETWEEN_LETTERS) {
      //print("timeSinceLastChange = "); println(timeSinceLastChange);
      translateMorseToLetter(lastSignsInLetter);
      lastSignsInLetter = "";
    }
    
    // new word
    if (timeSinceLastChange > MIN_TIME_BETWEEN_WORDS) {
      println(" NEW WORD \n\n\n");
    }
  }

  lastChangeTime = millis();

}

void translateMorseToLetter(String letterInMorse) {
      print("end of letter: ");
      print(letterInMorse);
      for (int i=0; i < SIZE ;  i++) {
        if (letterInMorse == letters[i]) {
          print (" letter num: ");
          print (i);
          print (" char: ");
          char theChar[1];
          sprintf(theChar, "%c", (i+65));
          print (theChar);
          //Serial.write('0' + (i+65));
        }
      }
      println("\n");
}

void print (int s) {
  Serial.print(s);
}

void println (int s) {
  Serial.print(s);
  Serial.println("");
}

void print (String s) {
  Serial.print(s);
}

void println (String s) {
  Serial.print(s);
  Serial.println("");
}