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 /* Arduino active sonar with metal detector style buzzer response */
 
 // Libraries, external functions
 #include <NewPing_mod.h>
 #include <EEPROM_Int_ReadWrite>
 
 // Configuration constants
 const unsigned int BAUD_RATE = 9600; // Serial communication rate (Bd)
 const unsigned int STATUS_PIN = 13; // Pin identifier of internal LED
 const unsigned int BUZZ_PIN = 12; // Pin identifier of buzzer output
 const unsigned int SONAR_TRIG_PIN = 7; // Pin identifier of sonar output (can be the same as echo pin)
 const unsigned int SONAR_ECHO_PIN = 8; // Pin identifier of sonar input (can be the same as trigger pin)
 const unsigned int BUZZ_LENGTH = 80; // Duration of a buzz (ms)
 const unsigned int PULSE_LENGTH = 10; // Duration of outgoing trigger signal (us)
 const unsigned int PULSE_SAMPLES = 1; // Number of sonar pulses to take a statistical mean from (potentially interferes with buzz timing at high frequencies)
 const unsigned int PULSE_SKIP = 3; // Number of measurements to discard from start of execution, because the initial responses are off sometimes
 const unsigned int PULSE_DELAY = 500; // Amount of time between sonar queries (ms)
 const unsigned int MAX_DISTANCE = 900; // Maxium distance to probe for (cm)
 const unsigned int LOW_DISTANCE = 5 * US_ROUNDTRIP_CM; // Response time corresponding to a solid tone (us)
 const unsigned int HIGH_DISTANCE = 350 * US_ROUNDTRIP_CM; // Response time corresponding to highest buzz delay (us)
 const unsigned int MAX_BUZZ_DELAY = 5000; // Buzz delay to use with highest distance (ms)
 const unsigned int MIN_BUZZ_DELAY = 150; // Buzz delay to use with lowest distance (ms)
 const signed int RECORD_ADDR = 0; // Use this EEPROM address (occupies 2 bytes) to save maximum measured distance (negative value to disable)
 const bool BUZZ_ENABLED = true; // Use the buzzer to report distance metal detector style
 const bool STATUS_ENABLED = true; // Use the status led in addition to / instead of buzzer beeps
 
 // Internal constants and variables
 const float DISTANCE_RANGE = HIGH_DISTANCE - LOW_DISTANCE; // Range in which to vary buzz delay (us)
 const unsigned int BUZZ_DELAY_RANGE = MAX_BUZZ_DELAY - MIN_BUZZ_DELAY; // Range of values for buzz delay (ms)
 unsigned long buzzDelay = 0; // Delay between buzzes (ms)
 unsigned long lastBuzz = 1; // Historical timestamp of most recent buzz (ms)
 unsigned long nextPulse = 1; // Timestamp for next sonar pulse (ms)
 unsigned long pulseCount = 0; // Number of queries performed from start of execution
 unsigned int recordDistance = 0; // Highest distance measured (us)
 NewPing sonar(SONAR_TRIG_PIN, SONAR_ECHO_PIN, MAX_DISTANCE); // NewPing sonar interface
 
 void setup() {
 
  // Set up output pins
  pinMode(STATUS_PIN, OUTPUT);
  pinMode(BUZZ_PIN, OUTPUT);
 
  // Make sure outputs are low
  digitalWrite(STATUS_PIN, LOW);
  digitalWrite(BUZZ_PIN, LOW);
 
  // Start serial connection
  Serial.begin(BAUD_RATE);
 
  // Read and report current record
  if (RECORD_ADDR > -1) {
   recordDistance = EEPROMReadInt(RECORD_ADDR);
   if (recordDistance > 0xFF00) recordDistance = 0; // Reset uninitialized or faulty value
    Serial.print("Current record is ");
    outputDistance(recordDistance);
    Serial.println();
  }
 
 }
 
 void loop() {
 
  // Read current Arduino timestamp
  unsigned long arduinoTime = millis();
 
  // Start a new buzz (solid tone)
  if (buzzDelay == 1 && digitalRead(BUZZ_PIN) == LOW) {
    startBuzz();
 
  // Start a new buzz (single beep)
  } else if (buzzDelay != 0 && arduinoTime > lastBuzz + buzzDelay) {
 
     startBuzz();
 
     // Schedule the buzz end and next buzz
     NewPing::timer_ms(BUZZ_LENGTH, stopBuzz);
     lastBuzz = arduinoTime;
 
   }
 
  // Query the ultrasonic sensor
  if (nextPulse != 0 && arduinoTime > nextPulse) {
 
   // Read and filter the sensor data
   unsigned int responseTime = sonar.ping_median(PULSE_SAMPLES);
 
   // Update pulse count and proceed only if high enough
   if (++pulseCount > PULSE_SKIP) {
 
     // Report values to the serial port
     Serial.print("Measured ");
     outputDistance(responseTime);
     Serial.print(" (");
     Serial.print(pulseCount);
     Serial.println(")");
 
     // Update and report record
    if (RECORD_ADDR > -1 && responseTime > recordDistance) {
      recordDistance = responseTime;
      EEPROMWriteInt(RECORD_ADDR, responseTime);
      Serial.print("Wrote new record to ROM: ");
      outputDistance(recordDistance);
      Serial.println();
    }
 
     // Adjust buzz timing
     boolean solidTone = (buzzDelay == 1);
     if (responseTime == 0) {
      buzzDelay = 0;
     } else {
      if (responseTime <= LOW_DISTANCE) {
        buzzDelay = 1;
      }
      if (responseTime > LOW_DISTANCE && responseTime <= HIGH_DISTANCE) {
       buzzDelay = (responseTime - LOW_DISTANCE) / DISTANCE_RANGE * BUZZ_DELAY_RANGE + MIN_BUZZ_DELAY;
      }
      if (responseTime > HIGH_DISTANCE) {
       buzzDelay = MAX_BUZZ_DELAY;
      }
     }
     if (solidTone && buzzDelay != 1) stopBuzz();
 
   } else {
      Serial.print("Skipped measurement ");
      Serial.println(pulseCount);
   }
 
   // Schedule the next pulse
   nextPulse = arduinoTime + PULSE_DELAY;
 
  }
 
 }
 
 // Activate buzzer
 void startBuzz() {
   if (BUZZ_ENABLED) digitalWrite(BUZZ_PIN, HIGH);
   if (STATUS_ENABLED) digitalWrite(STATUS_PIN, HIGH);
 }
 
 // Stop an ongoing buzz
 void stopBuzz() {
   digitalWrite(BUZZ_PIN, LOW);
   digitalWrite(STATUS_PIN, LOW);
   NewPing::timer_stop();
 }
 
 // Output response time in human-readable format
-void outputDistance(int responseTime) {
+String outputDistance(int responseTime) {
   Serial.print(responseTime);
   Serial.print(' ');
   Serial.write(181); // Micro sign in ISO-8859-1
   Serial.print("s / ");
   Serial.print(sonar.convert_cm(responseTime));
   Serial.print(" cm");
 }