i2c_flowmeter.ino

#include <TinyWireS.h>

// MAX INT 32767


#ifndef TWI_RX_BUFFER_SIZE
#define TWI_RX_BUFFER_SIZE (16)
#endif

#define ADDR 0x11
#define PIN 3

// Flow meter Variables
uint8_t flowState = 0;
uint8_t lastFlowState = 0;

unsigned long lastTick;
unsigned long timeBetweenTicks = 0;
const int litersPerTick = 10;

float litersPerSec = 0;
uint8_t litersPerMin = 0;

/**
 * This is called for each read request we receive, never put more than one byte of data (with TinyWireS.send) to the 
 * send-buffer when using this callback
 */
void requestEvent()
{  
  TinyWireS.send(byte(litersPerMin)); // its a uint8_t so it can go as one byte.
  // Note this number can only be 0 - 255 (unsigned 8 bit), otherwise the payload has to be split into bytes and buffered in this function
  // Increment the reg position on each read, and loop back to zero
}

void setup() {
  TinyWireS.begin(ADDR);
  TinyWireS.onRequest(requestEvent);

  pinMode(PIN, INPUT);
}

void loop() {
  flowState = digitalRead(PIN);
  
  if (flowState != lastFlowState) {
    if (flowState == LOW) {
      
      unsigned long newTime = millis();
      
      timeBetweenTicks = newTime - lastTick;

      if(timeBetweenTicks > 1000) {
        lastTick = newTime;
        litersPerSec = litersPerTick / (timeBetweenTicks / 1000.0);
        litersPerMin = int(litersPerSec * 60);           
      }
      
    }
  }
  
  // save the current state as the last state,
  // for next time through the loop
  lastFlowState = flowState;

  /**
   * This is the only way we can detect stop condition (http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=984716&sid=82e9dc7299a8243b86cf7969dd41b5b5#984716)
   * it needs to be called in a very tight loop in order not to miss any (REMINDER: Do *not* use delay() anywhere, use tws_delay() instead).
   * It will call the function registered via TinyWireS.onReceive(); if there is data in the buffer on stop.
   */
  TinyWireS_stop_check();
}