title: numTicks variable not incrementing
body: <p>I have the following sketch, and the numTicks variable is not incrementing, the sketch compiles fine to the Arduino, but for whatever reason the variable "numTicks" is not incrementing.</p>
  
  <pre><code>/*
   * kegboard-clone-4-KegCop
   * This code is public domain
   *
   * This sketch sends a receives a multibyte String from the iPhone
   * and performs functions on it.
   *
   * This Arduino sketch is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU Public License
   * along with this sketch.  If not, see &lt;http://www.gnu.org/licenses/&gt;.
   * 
   * Examples:
   * http://arduino.cc/en/Tutorial/SerialEvent
   * http://arduino.cc/en/Serial/read
   * http://stackoverflow.com/questions/16532586/arduino-sketch-that-responds-to-certain-commands-how-is-it-done/
   * http://davebmiller.wordpress.com/2011/01/18/arduino-flowmeter/
   * http://forum.arduino.cc/index.php?topic=52003.0
   * http://arduino.cc/en/Reference/AttachInterrupt
   * https://github.com/just-kile/Zapfmaster2000/blob/master/src/zapfmaster2000-zapfkit-avr/draftkitAVR.ino
   *
   * TODO:
   * - eventually get code working with the SF800 flow sensor / flowmeter
   *
   */
  
  // flow_A LED
  int led = 4;
  
  // relay_A
  const int RELAY_A = A0;
  
  // string / serial event variables
  String inputString = ""; // a string to hold incoming data
  boolean stringComplete = false; // whether the string is complete
  boolean valve_open = false;
  
  // FLOWMETER SHIT
  // flowmeter 0 pulse (input) = digital pin 2
  // https://github.com/Kegbot/kegboard/blob/master/arduino/kegboard/kegboard_config.h
  // which pin to use for reading the sensor? kegboard-mini shield has digital pin 2 allocated
  // the SF800 outputs 5400 pulses per litre
  // The hall-effect flow sensor (SF800) outputs approximately 5400 pulses per second per litre/minute of flow
  // SF800 default (5400 ticks/Liter == 5.4 ticks/mL == 1/5.4 mL/tick)
  int flowmeterInterrupt = 0;  // changed from byte
  int flowmeterPin = 2;        // changed from byte
  int flowmeterPinState = 0;   // variable for storing state of sensor pin
  // read RPM
  int rpmcount = 0;
  int rpm = 0;
  unsigned long lastmillis = 0; 
  
  // NEW GLOBALS - 29JUL13
  // initial ticks on flow meter
  volatile unsigned int numTicks = 0;
  // interval for flow meter frequency
  int interval = 250;
  volatile long previousMillis = 0;
  
  void setup() {
    // initialize serial
  //  Serial.flush(); // flush the serial buffer on setup.
    Serial.begin(115200); // open serial port, sets data rate to 9600bps
    Serial.println("Power on test");
    inputString.reserve(200);
    valve_open = false;
  
    // relay for solenoid cut off valve
    pinMode(RELAY_A, OUTPUT);
  
    // flowmeter shit
    pinMode(flowmeterPin, INPUT);
    digitalWrite(flowmeterPin, HIGH); // Need to set these HIGH so they won't just tick away
  
    // The Hall-effect sensor is connected to pin 2 which uses interrupt 0.
    // Configured to trigger on a RISING state change (transition from HIGH
    // state to LOW state)
    attachInterrupt(flowmeterInterrupt, count, RISING);
  }
  
  void open_valve() {
    digitalWrite(RELAY_A, HIGH); // turn RELAY_A on
    valve_open = true;
  }
  
  void close_valve() {
    digitalWrite(RELAY_A, LOW); // turn RELAY_A off
    valve_open = false;
  }
  
  void flow_A_blink() {
    digitalWrite(led, HIGH); // turn the LED on (HIGH is the voltage level)
    delay(1000);              // wait for one second
    digitalWrite(led, LOW);   // turn the LED off by making the voltage LOW
    delay(1000);              // wait for a second
  }
  
  void flow_A_blink_stop() {
    digitalWrite(led, LOW);
  }
  
  void flow_A_on() {
    digitalWrite(led, HIGH); // turn the LED on (HIGH is the voltage level)
  }
  
  void flow_A_off() {
    digitalWrite(led, LOW);   // turn the LED off by making the voltage LOW
  }  
  
  // flowmeter shit
  void getFlow4() {
  //  Serial.println("im here");
  //  Serial.println(sensorPin);
  
    flowmeterPinState = digitalRead(flowmeterPin);
  
  //  Serial.println(sensorPinState);
  
    volatile unsigned long currentMillis = millis();
    // if the predefined interval has passed
    if(currentMillis - previousMillis &gt; interval) { // Uptade every 1/4 second, this will be equal to reading frecuency (Hz).
  
      // disconnect flow meter from interrupt
      detachInterrupt(flowmeterInterrupt); // Disable interrupt when calculating
      // check, whether any flow was detected
      if (numTicks &gt;= 0) {
        // start message to computer with tick message symbol
        Serial.print("Ticks:");
        // send amount of ticks for last interval
        Serial.print(numTicks);
      }
      // clean buffer
      Serial.flush();
      // reset amount of ticks
      numTicks = 0;
      // set new start value for interval counter
      previousMillis = currentMillis;
      // reattach interrupt
      attachInterrupt(flowmeterInterrupt, count, RISING);
    }
  
  
    if(flowmeterPinState == LOW) {
      flow_A_off();
  //    Serial.println("don't blink");
    }
    if(flowmeterPinState == HIGH) {
      flow_A_on();
  //    Serial.println("blink damnit");
    }
  
    if(stringComplete) {
      if(inputString.equals("{close_valve}\n")) {
        //      Serial.println("close vavle.");
        close_valve();
      }
      return;
    }
  }
  // flow meter interrupt function
  void count(){
    numTicks++;
  } 
  
  /*
   * Main program loop, runs over and over repeatedly
   */
  
  void loop() {
    if(stringComplete) {
  //    Serial.println(inputString);
  
      if(inputString.equals("{open_valve}\n")) {
  //      Serial.println("inputString equates :)");
        open_valve();
      }
  
      if(inputString.equals("{close_valve}\n")) {
        //      Serial.println("close vavle.");
        close_valve();
      }
  
    if(valve_open) {
  //    Serial.println("valve_open = true");
      inputString = "";
      stringComplete = false;
      while(numTicks &lt;= 1000) {
        getFlow4();
      }
    }
  
    // clear the string:
    inputString = "";
    stringComplete = false;
    }
  //Serial.println("over and over");
  }
  
  /*
   SerialEvent occurs whenever a new data comes in the
   hardware serial RX.  This routine is run between each
   time loop() runs, so using delay inside loop can delay
   response.  Multiple bytes of data may be available.
   */
  
  void serialEvent() {
    while(Serial.available()) {
      // get the new byte:
      char inChar = (char)Serial.read();
      // add it to the inputString:
      inputString += inChar;
      // if the incoming character is a newline, set a flag
      // so the main loop can do something about it:
      if (inChar == '\n') {
        stringComplete = true;
      }
      // Serial.println(inputString.length());
    }
  }
  </code></pre>