const int ledPin = 13;
int previousA0Value = 0;
  
void setup()
{
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}


void loop()
{
  int A0value = analogRead(A0);
  if ( A0value != previousA0Value ) {
    Serial.print("value = "); Serial.println(A0value);
    previousA0Value = A0value;
  }
  digitalWrite(ledPin, HIGH); delay(500);
  digitalWrite(ledPin, LOW); delay(500);
}

byte readIDSwitch(){

  byte id;
  // this table is derived from measuring voltages / resistance
  // from the resistor ladder circuit
  const int id_table[] = {
    0, 114, 205, 279,    //0,   1,   2,   3 
    341, 394, 438, 477,  //4,   5,   6,   7 
    512, 542, 568, 592,  //8,   9,  10,  11 
    614, 633, 651, 667   //12, 13,  14,  15 
  };
  const int epsilon = 10;

  short v = analogRead(A0); //Wherever the signal goes to from resistors
  Serial.println("buttons " + String(v) );
  
  // use a lookup table, because the voltages are not linear
  for (int i = 0 ; i < 16; i++ ) {
    if ( (id_table[i] - epsilon < v) &&
            (v < id_table[i] + epsilon) ) {
        id = i;
        Serial.println("id " + String(id) );
        return id;
    }
  }
  return 0;
}