I = V / R
I = 5 / 330 = 0.015
I = 15 mA

void powerOnPeripherals ()
  {
  digitalWrite (POWER, LOW);  // turn power ON
  delay (1); // give time to power up    
  }  // end of powerOnPeripherals

2900000 / 6 = 483333 hours
2900000 / 6 / 24 / 30 = 671 months

1 / (15 * 60 / .128) = 0.000142

1 / (15 * 60 / .128) * 250 = 0.0355 mA

// DHT-22 temperature and humidity sensor
DHT dht (DHTPIN, DHTTYPE, 3);    // 6 for 16 MHz, 3 for 8 Mhz (defines pulse width for zero/one)

// temp. for nominal resistance (almost always 25 C) 
const int TEMPERATURENOMINAL = 25;

// resistance at TEMPERATURENOMINAL (above)
const int THERMISTORNOMINAL = 5000;

// The beta coefficient of the thermistor (usually 3000-4000) 
const int BCOEFFICIENT = 3960;

// the value of the 'other' resistor (measure to make sure)
const int SERIESRESISTOR = 4644;

  ADMUX = 0;  // turn off internal Vref

    case 'A':          converted = 0b1110111;  break;  
    case 'b':          converted = 0b0011111;  break;  
    case 'c':          converted = 0b0001101;  break;  
    case 'C':          converted = 0b1001111;  break;  
    case 'd':          converted = 0b0111101;  break;  
    case 'E':          converted = 0b1001111;  break;  

void loop () 
  {
  // sleep for 8 seconds
  myWatchdogEnable (WDT_8_SEC);

  // did they push the switch?
  if (buttonPressed)
    showStuff ();
    
  // count number of times we slept
  counter++;

  // every 48 seconds check the time (6 lots of 8 seconds asleep)
  if (counter >= 6)
    {  
    powerOnPeripherals ();
    getTime ();
    if (now.minute () != lastMinute)
      {
      if ((now.minute () % TAKE_READINGS_EVERY) == 0)
        recordReading ();
      lastMinute = now.minute ();
      }  // end of change in the minute
    powerOffPeripherals ();
      
    counter = 0;
    }  // end of sleeping for 6 times
    
}  // end of loop

2013-08-06 09:00:40	47.20	18.30	18.85	6.87	518

YYYY-MM-DD HH:MM:SS    Humidity Temp1   Temp2    Dew    Light  
-- Date -- - Time -        %      C       C       C     0 - 1023  

// Set date/time on Temperature / Humidity / Light level logger
//
// Author: Nick Gammon
// Date:   6 August 2013

// Use Lilypad Arduino w / Atmega328 board type

#include <Wire.h>
#include <RTClib.h>

const byte POWER = 3;
// const byte DS1307_ADDRESS = 0x68;  // for checking clock there (I2C address)

RTC_DS1307 RTC;

void setup () 
  {
  Serial.begin (115200);
  Serial.println ();
  Serial.println ("Setting the date/time to: " __DATE__ " " __TIME__);
  
  // power MOSFET - initially off
  pinMode      (POWER, OUTPUT);
  digitalWrite (POWER, LOW);  // turn power ON
  delay (1); // give time to power up    

  Wire.begin ();
  RTC.begin ();
  delay (2);
  TWBR = 72;  // 50 kHz at 8 MHz clock
  
  // check RTC is on I2C bus
  Wire.beginTransmission (DS1307_ADDRESS);
  Wire.write ((byte) 0);	
  if (Wire.endTransmission () != 0)
    {
    Serial.println  ("Cannot find Real Time Clock");
    return;
    }

  // check RTC clock responds
  if (Wire.requestFrom (DS1307_ADDRESS, 1) != 1)
    {
    Serial.println  ("Real Time Clock not responding");
    return;
    }

  // read and discard that one byte
  Wire.read ();
  
  RTC.adjust (DateTime(__DATE__, __TIME__));
  Serial.println ("Time set.");
  }  // end of setup

void loop () {}

# Data file uses tab as a separator
set datafile separator '\t'

# Title of the plot
set title "Temperature and humidity plot"

# We want a grid
set grid

# X-axis label
set xlabel "Date/Time"

# Use automatic scaling
set autoscale

# Title for Y-axis
set ylabel "Temperature (C)"

# Title for Y2-axis
set y2label "Humidity (%)"

# place ticks on second Y2-axis
set y2tics border

# Define that data on X-axis should be interpreted as time
set xdata time

# Time in log-file is given in format YYYY-MM-DD HH:MM:SS
set timefmt "%Y-%m-%d %H:%M:%S"

# Display notation for time
set format x "%d %b\n%Y"

# generate a legend which is placed underneath the plot
set key outside bottom center box title "Temperature Sensor"

# output into png file
set terminal png size 800,500
set output "plot.png"

# Data columns are:
# 1 is date/time
# 2 is humidity
# 3 is temperature
# 4 is temperature (second sensor)
# 5 is dew point
# 6 is light

# Below, "using 1:2" means use column 1 of the data for X, and column 2 of the data for Y

# read data from file and generate plot
plot "READINGS.TXT" using 1:3 title "Temperature (C)" with lines axes x1y1 \
  , "" using 1:2 title "Relative Humidity (%)" with lines axes x1y2

gnuplot (filename)