Arduino Sketch for data logging water flow to an SD card. Project at http://thomasloughlin.com/rain-water-collection/.

RainWaterOutputLogger.pde

#include <SD.h>
/*
 This script is a simple combination of two existing example files.
 The goal is to measure water flow coming from a rain collection barrel 
 The project progress can be found at http://thomasloughlin.com/rain-water-collection/.

*/
/**********************************************************
This is example code for using the Adafruit liquid flow meters. 

Tested and works great with the Adafruit plastic and brass meters
    ------> http://www.adafruit.com/products/828
    ------> http://www.adafruit.com/products/833

Connect the red wire to +5V, 
the black wire to common ground 
and the yellow sensor wire to pin #2

Adafruit invests time and resources providing this open source code, 
please support Adafruit and open-source hardware by purchasing 
products from Adafruit!

Written by Limor Fried/Ladyada  for Adafruit Industries.  
BSD license, check license.txt for more information
All text above must be included in any redistribution
**********************************************************/
/*
  SD card datalogger
 
 This example shows how to log data from three analog sensors 
 to an SD card using the SD library.
   
 The circuit:
 * analog sensors on analog ins 0, 1, and 2
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11
 ** MISO - pin 12
 ** CLK - pin 13
 ** CS - pin 4
 
 created  24 Nov 2010
 modified 9 Apr 2012
 by Tom Igoe
 
 This example code is in the public domain.
 	 
 */
// which pin to use for reading the sensor? can use any pin!
#define FLOWSENSORPIN 2
const int chipSelect = 4;

// count how many pulses!
volatile uint16_t pulses = 0;
// track the state of the pulse pin
volatile uint8_t lastflowpinstate;
// you can try to keep time of how long it is between pulses
volatile uint32_t lastflowratetimer = 0;
// and use that to calculate a flow rate
volatile float flowrate;
// Interrupt is called once a millisecond, looks for any pulses from the sensor!
SIGNAL(TIMER0_COMPA_vect) {
  uint8_t x = digitalRead(FLOWSENSORPIN);
  
  if (x == lastflowpinstate) {
    lastflowratetimer++;
    return; // nothing changed!
  }
  
  if (x == HIGH) {
    //low to high transition!
    pulses++;
  }
  lastflowpinstate = x;
  flowrate = 1000.0;
  flowrate /= lastflowratetimer;  // in hertz
  lastflowratetimer = 0;
}

void useInterrupt(boolean v) {
  if (v) {
    // Timer0 is already used for millis() - we'll just interrupt somewhere
    // in the middle and call the "Compare A" function above
    OCR0A = 0xAF;
    TIMSK0 |= _BV(OCIE0A);
  } else {
    // do not call the interrupt function COMPA anymore
    TIMSK0 &= ~_BV(OCIE0A);
  }
}

void setup() {
   Serial.begin(9600);
   Serial.println("Flow sensor test!");
   //lcd.begin(16, 2);
   Serial.println("Initializing SD card...");
  // make sure that the default chip select pin is set to
  // output, even if you don't use it:
  pinMode(10, OUTPUT);
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    return;
  }
  Serial.println("card initialized.");
   
   pinMode(FLOWSENSORPIN, INPUT);
   digitalWrite(FLOWSENSORPIN, HIGH);
   lastflowpinstate = digitalRead(FLOWSENSORPIN);
   useInterrupt(true);
}

void loop()                     // run over and over again
{ 
  //lcd.setCursor(0, 0);
  //Serial.print("Pulses:"); Serial.print(pulses, DEC);
  //Serial.print(" Hz:");
  //Serial.print(flowrate);
  //lcd.print(flowrate);
  Serial.print("Freq: "); Serial.println(flowrate);
  Serial.print("Pulses: "); Serial.println(pulses, DEC);
  
  // if a plastic sensor use the following calculation
  // Sensor Frequency (Hz) = 7.5 * Q (Liters/min)
  // Liters = Q * time elapsed (seconds) / 60 (seconds/minute)
  // Liters = (Frequency (Pulses/second) / 7.5) * time elapsed (seconds) / 60
  // Liters = Pulses / (7.5 * 60)
  float liters = pulses;
  liters /= 7.5;
  liters /= 60.0;


  Serial.print(liters); Serial.println(" Liters");
  
  float gallons=liters * 0.2642;
  Serial.print(gallons); Serial.println(" Gallons");
  
    File dataFile = SD.open("datalog.txt", FILE_WRITE);

  // if the file is available, write to it:
  if (dataFile) {
    dataFile.print("Liters: ");
    dataFile.print(liters);
    dataFile.print(" Gallons: ");
    dataFile.println(gallons);
    dataFile.close();
    // print to the serial port too:
    //Serial.println(dataString);
  }  
  // if the file isn't open, pop up an error:
  else {
    Serial.println("error opening datalog.txt");
  } 
 
  delay(100);
}