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Source code

/*
 * 使用 1 個 PIN 判斷 16 個 KEY 的 INPUT
 *
 */

#define key_pin 0  // define key sensor pin
#define key_val_size 11 // define key value's size
int key_val[key_val_size] = {0};  // store key sensor value
byte index = 0;  // key sensor array's index
byte button_up_count = 0;
boolean is_button_down = 0;

void setup()
{
  Serial.begin(9600);
}

void loop()
{
  if(analogRead(key_pin)  > 215 && analogRead(key_pin) < 610 && index < key_val_size)
  {
    is_button_down = 1;
    key_val[index++] = analogRead(key_pin);
  }
  else if(analogRead(key_pin) == 0)
  {
    button_up_count++;
    if (button_up_count > 5 && is_button_down == 1)
    {
      index = 0;
      button_up_count = 0;
      is_button_down = 0;
      switch ( detectKey() )
      {
        case 1:
          Serial.println("key 1");
          break;
        case 2:
          Serial.println("key 2");
          break;
        case 3:
          Serial.println("key 3");
          break;
        case 4:
          Serial.println("key 4");
          break;
        case 5:
          Serial.println("key 5");
          break;  
        case 6:
          Serial.println("key 6");
          break;  
        case 7:
          Serial.println("key 7");
          break;  
        case 8:
          Serial.println("key 8");
          break;  
        case 9:
          Serial.println("key 9");
          break;  
        case 10:
          Serial.println("key 10");
          break;  
        case 11:
          Serial.println("key 11");
          break;  
        case 12:
          Serial.println("key 12");
          break;  
        case 13:
          Serial.println("key 13");
          break;  
        case 14:
          Serial.println("key 14");
          break;  
        case 15:
          Serial.println("key 15");
          break;  
        case 16:
          Serial.println("key 16");
          break;  
        default:
          break;
      }  // end of switch
    }  // end of if
  }

}

byte detectKey()
{
  for (byte i = 0; i < key_val_size; i++)
  {
    for (byte j = i+1; j < key_val_size; j++)
    {
      if (key_val[i] > key_val[j])
      {
        int temp = key_val[i];
        key_val[i] = key_val[j];
        key_val[j] = temp;
      }
    }
  }
  
  int average_val = key_val[key_val_size - 2];
  for (byte i = 0; i < key_val_size; i++)
    key_val[i] = 0;
  if (average_val < 216)
    return 0;
  else if (average_val < 234)
    return 13;
  else if (average_val < 247)
    return 14;
  else if (average_val < 257)
    return 15;
  else if (average_val < 263)
    return 16;
  else if (average_val < 275)
    return 9;
  else if (average_val < 293)
    return 10;
  else if (average_val < 307)
    return 11;
  else if (average_val < 326)
    return 12;
  else if (average_val < 356)
    return 5;
  else if (average_val < 387)
    return 6;
  else if (average_val < 412)
    return 7;
  else if (average_val < 434)
    return 8;
  else if (average_val < 475)
    return 1;
  else if (average_val < 530)
    return 2;
  else if (average_val < 578)
    return 3;
  else if (average_val < 611)
    return 4;
}