Sending float array through I2C from Arduino to RPi

i2c-arduino.ino

#include <Wire.h>

#define SLAVE_ADDRESS 0x04
#define FLOATS_SENT 3

float data[FLOATS_SENT];

void setup() {
  pinMode(13, OUTPUT);
  Serial.begin(9600); // start serial for output
  // initialize i2c as slave
  Wire.begin(SLAVE_ADDRESS);

  // define callbacks for i2c communication
  //Wire.onReceive(receiveData);
  Wire.onRequest(sendData);

  Serial.println("Ready!");
}

void loop() {
  delay(1000);
}

/* callback for received data */
void receiveData(int byteCount) {
  while (Wire.available()) {
    status = Wire.read();
    Serial.print("data received: ");
    Serial.println(status);

    if (status == 1) {

      if (state == 0) {
        digitalWrite(13, HIGH); // set the LED on
        state = 1;
      }
      else {
        digitalWrite(13, LOW); // set the LED off
        state = 0;
      }
    }
  }
}

// callback for sending data
void sendData() {
  data[0] = getWindspeed(A0);
  data[1] = getLuminosity(A1);
  data[2] = getRainRes(A2);
  Wire.write((byte*) &data, FLOATS_SENT*sizeof(float));
}

float getWindspeed(byte pin) {
  int sensorValue = analogRead(pin);
  float outVoltage = sensorValue * (5.0 / 1023);
  return outVoltage*6;
}

int getLuminosity(byte pin) {
  int sensorValue = analogRead(pin);
  return sensorValue;
}

int getRainRes(byte pin) {
  int sensorValue = analogRead(pin);
  return sensorValue;  
}

i2c-rpi.py

#!/usr/bin/env python
# coding: utf8

import smbus
import struct
import time
import requests
# for RPI version 1, use "bus = smbus.SMBus(0)"
bus = smbus.SMBus(1)

# This is the address we setup in the Arduino Program
address = 0x04

# Set the request parameters
urlPimatic = 'http://home.keno.lan:1607/api/variables/'
urlEmon = 'http://home.keno.lan/emoncms/input/post.json'
apiKey = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
user = 'user'
pwd = 'pass'

PROGRAM_NAME_VERSION = "I2C Reader v4.6.9"
DEBUG = True

# Set proper headers
headers = {"Content-Type":"application/json","Accept":"application/json"}

utime = time.time()
pausePatching = 1   #time in seconds for patching variables
thWind = 1.8        #threshold km/h value for patching variables
thLight = 0         #threshold for luminosity
thRain = 0          #threshold for rain sensor
oldValWind = 0.01
oldValLight = 0.01
oldValRain = 0.01
isPatchedWind = False
isPatchedLight = False
isPatchedRain = False
previousSecs = 0
retry = 0

def splashScreen(name):
 print "   __                 ____     _____ "
 print "  / /_____ ___  ___  / __/__  / _/ /_"
 print " /  '_/ -_) _ \/ _ \_\ \/ _ \/ _/ __/"
 print "/_/\_\\__/_//_/\___/___/\___/_/ \__/ "
 print "                          %s         " % name
 time.sleep(1)

def patchVarWind(val, var, threshold=0, node=False):
 global oldValWind, isPatchedWind
 print "Windmesser %f" % val
 if((abs(val-oldValWind) >= threshold) or isPatchedWind == False):
  if DEBUG: print "patching %s - %f" % (var, val)
  # Do the HTTP request
  oldValWind = val
  isPatchedWind = True
  requests.patch(urlPimatic+var, auth=(user, pwd), headers=headers ,data='{"type":"value", "valueOrExpression": "%.2f"}' % val)
  if(node):
   requests.get("%s?node=%d&json={windspeed:%.2f}&apikey=%s" % (urlEmon, node, val, apiKey), auth=(user, pwd)) 
 
def patchVarLight(val, var, varString, threshold=0, node=False):
 global oldValLight, isPatchedLight
 if DEBUG: print "Light: %f" % val
 if(abs(val-oldValLight) >= threshold or isPatchedLight == False):
  if DEBUG: print "patching %s - %f" % (var, val)
  # Do the HTTP request
  oldValLight = val
  isPatchedLight = True
  requests.patch(urlPimatic+var, auth=(user, pwd), headers=headers ,data='{"type":"value", "valueOrExpression": "%.2f"}' % val)
  requests.patch(urlPimatic+varString, auth=(user, pwd), headers=headers ,data='{"type":"value", "valueOrExpression": "%s"}' % convLightToStr(val))
  if(node):
   requests.get("%s?node=%d&json={windspeed:%.2f}&apikey=%s" % (urlEmon, node, val, apiKey), auth=(user, pwd))

def patchVarRain(val, var, threshold=0, node=False):
 global oldValRain, isPatchedRain
 print "Windmesser %f" % val
 if((abs(val-oldValWind) >= threshold) or isPatchedWind == False):
  if DEBUG: print "patching %s - %f" % (var, val)
  # Do the HTTP request
  oldValWind = val
  isPatchedWind = True
  requests.patch(urlPimatic+var, auth=(user, pwd), headers=headers ,data='{"type":"value", "valueOrExpression": "%.2f"}' % val)
  if(node):
   requests.get("%s?node=%d&json={windspeed:%.2f}&apikey=%s" % (urlEmon, node, val, apiKey), auth=(user, pwd))
   
def convLightToStr(val):
 if(val <= 11): return "sonnig"
 elif(val >= 12 and val <= 100): return "wolkig"
 elif(val >= 101 and val <= 470): return "daemmerung"
 elif(val >= 671): return "nacht"
 else: return "unknown"
 
def convRainToStr(val):
 if(val <= 800): return "regen"
 elif(val > 800): return "trocken"

def get_data():
    return bus.read_i2c_block_data(address, 0);

def get_float(data, index):
    bytes = data[4*index:(index+1)*4]
    return struct.unpack('f', "".join(map(chr, bytes)))[0]

## Begin ##
splashScreen(PROGRAM_NAME_VERSION)

while True:
 try:
  if (retry > 2):
   time.sleep(30)
  elif(retry > 5):
   time.sleep(60)

  data = get_data()
  
  dataWind = get_float(data, 0)*3.6
  patchVarWind(dataWind, 'aussen-windmesser', thWind, 10) # x3.6 for km/h instead of m/s
  
  dataLight = get_float(data, 1)
  if (dataLight > 900):
   interval = 600
   thLight = 20
  elif (dataLight > 50):
   interval = 60
   thLight = 5
  elif (dataLight > 13):
   interval = 60
   thLight = 4
  else:
   interval = 60
   thLight = 1
  currentSecs = int(time.time())  
  if(currentSecs - previousSecs > interval):
   previousSecs = currentSecs
   patchVarLight(dataLight, 'garten-lichtsensor', 'system-lichtsensor', thLight) #

 except KeyboardInterrupt:
  print "Abbruch durch Benutzer"
 except requests.exceptions.ConnectionError as e:
  print "Fehler bei der Verbindung zur Domain %s!" % url
  time.sleep(10)
  retry += 1
 except requests.exceptions.ConnectTimeout as e:
  print "Zeitüberschreitung der Verbindung!"
 except IOError:
  time.sleep(10)
 time.sleep(1)