The document summarizes how to create a data logger using an Arduino board. It describes connecting sensors like a barometric pressure sensor and LCD display to log weather data over time to an SD card. Libraries are used to interface with the sensors and SD card. Code examples show how to record time-stamped sensor readings every 6 minutes to the SD card in CSV format.

1. Datalogging on an Arduino
DESERT CODE CAMP 2013.1
Presented by Don Doerres
Embedded Pro Guy
don@azlaborlaw.com

2. TODAY’S TAKEAWAYS
 The Arduino is a good starting point for a
data logger, a device used to obtain and
store data over a long period of time
 The Arduino with a few add-ins is capable of
 Storing data with time tags
 Displaying data in real time
 Doing these tasks without tying up a bigger
computer

3. IDEA WAS TO LOG WEATHER
 I started with a barometer (BMP085) and a
humidity sensor (DHT11)
 Both of these also provide temperature
information
 Power came from a desktop computer
through USB cable to Arduino, Arduino to
breadboard

4. FIRST BREADBOARD

5. SERIOUS WEATHER…

6. WEATHER WATCHING…
 Observing an approaching dust storm, I
realized that I didn’t want to leave the
computer or sensors outside
 Barometric pressure turned out to be
adequate for storm tracking
 Indoors, humidity did not change much
 So, I decided to record barometric pressure
and temperature

7. ORIGINALLY USED PC
 Used Tera Term (Terminal Emulator) to log
data
 Tera Term added time stamp from PC clock
 Once prototype was working, wanted to
move time keeping function and data logging
to Arduino and not tie up PC

8. ARDUINO TIMING SIX MINUTES,
WRITING TO SERIAL PORT
Tera Term Screen
Tera Term Log File—Adds Time Stamp

9. ORIGINAL PLAN: CHRONODOT & SD BREAKOUT
 Chronodot is a highly accurate clock with
battery backup
 SD Breakout allows simple connection to SD
card
 However, the combination would simply not
fit on an Arduino breakout shield, let alone
any sensors

10. DOT AND SD ON ARDUINO BREADBOARD
Dot
SD
breakout
 This picture shows the Dot and the SD card breakout
 This works as a breadboard, but is too big for a
shield

11. ADAFRUIT INTRODUCED A DATA LOGGER SHIELD
 About the time I realized that my logger
would not fit on a prototype shield, Adafruit
introduced their new logger shield
 This had a slightly lower accuracy clock than
the Dot, but it had everything else in surface
mount parts
 All I had to do was add the pressure sensor
and a connection to a 16X2 LCD display

12. ADAFRUIT LOGGER SHIELD
Battery Holder
SD Holder
DS1307 RTC
 Adafruit logger shield
 Surface mount parts left prototype area quite large
enough for sensors
 Add an I2C 16X2 LCD display

13. SENSOR SELECTION
 This is the BMP085 pressure sensor
 This is a sensitive barometer/altimeter and
temperature sensor
 It runs on 5V
 It has an I2C interface

14. I2C BUS
 This is a very simple serial Inter-Integrated
Circuit connection bus, hence I2C
 The interface consists of Clock, Data, and
ground
 Multiple devices can be hooked to the same
bus as long as they have different addresses
 The devices I used, pressure sensor
(address 0x77) and display (address 0), do
have different addresses

15. BMP085 CONNECTION TO ARDUINO

16. 16X2 LCD DISPLAY WITH I2C BACKPACK
 This is a back view showing the four wire
connections—same connections as BMP085
GND To GND
DAT to A4
CLK to A5
5V To 5V

17. OTHER CONNECTIONS
 The SD breakout and the Clock are already
wired up on the shield
 The pressure sensor I soldered to the I2C
connection pads on the shield
 The LCD display I simply plugged in to the
shield
 The BMP and the LCD display have different
I2C addresses, so there is no conflict

18. TYPICAL DISPLAY
 Date (Year not shown), local time
 Temperature in F, Pressure in mmHG
 Display updates every 5 seconds
 Data is stored to SD card every 6 minutes

19. WHAT GOES ON THE SD CARD
 The log is Comma Separated Values (CSV)
of Time, Temperature, Pressure
 Time is stored as a ‘C’ time stamp (more
about this in two slides)
 Temperature is degrees F
 Pressure is in millimeters of Mercury (mmHg)

20. SAMPLE OF LOG FILE
1363516494,79.0,691.0
1363516868,79.0,691.0
1363517243,79.0,691.0
1363517617,79.1,691.1
1363517991,79.1,691.1
1363518365,79.1,691.1
1363518740,79.1,691.1
1363519114,79.2,691.2
1363519488,79.2,691.2
1363519862,79.2,691.2
1363520237,79.2,691.2
1363520611,79.1,691.1
1363520985,79.2,691.2
1363521359,79.1,691.1
1363521734,79.1,691.1
1363522108,79.2,691.2
1363522482,79.2,691.2
1363522857,79.2,691.2
1363523231,79.2,691.2
1363523605,79.2,691.2
1363523979,79.2,691.2
1363524354,79.2,691.2
1363524728,79.1,691.1
1363525102,79.1,691.1
1363525476,79.1,691.1

21. THE CTIME STAMP
 The C language uses as a time stamp the
number of seconds since January 1, 1970
 A 32 bit signed integer allows counting
seconds until January 19, 2038 at 03:14:07
GMT
 …by then, we will likely switch to 64 bit
integers
 And, yes, the value is a signed integer so
that comparisons can be readily made

22. DISPLAYING IN EXCEL OR OTHER SPREADSHEET
 It is simple to convert ctime to Excel time
 The macro is, using ‘A2’ as a sample cell:
=DATE(1970,1,1)+(A2)/86400
 Display format is controlled with Excel
formatting
CTIME Increase Delta Day Date Time Deg F mmHg
1363504243 0 0 Sun Mar 17, 2013 07:10:43 74.2 691.2
1363506389 2146 2146 Sun Mar 17, 2013 07:46:29 75.4 691.4
1363506764 2521 375 Sun Mar 17, 2013 07:52:44 76.7 691.7
1363507138 2895 374 Sun Mar 17, 2013 07:58:58 77.5 691.5
1363507512 3269 374 Sun Mar 17, 2013 08:05:12 77.4 691.4
1363507886 3643 374 Sun Mar 17, 2013 08:11:26 77.3 691.3
1363508261 4018 375 Sun Mar 17, 2013 08:17:41 77.3 691.3

23. LIBRARIES

24. UNITS
 The units of the BMP085 pressure sensor
are Degrees C and pressure in Pascals
 Conversions are in order
tempy = bmp.readTemperature();
tempy = (tempy * 9.0 / 5.0) + 32.0;
press = bmp.readPressure();
fpress = (float)press* 0.007500616827042;

25. TIMESET.INO, 1 OF 2
// timeSet.ino
#include <Wire.h>
#include <RTClib.h>
#include <LiquidCrystal.h>
LiquidCrystal lcd(0);
RTC_DS1307 RTC;
DateTime now;
void setup()
{
Serial.begin(57600);
Wire.begin();
RTC.begin();
RTC.adjust(DateTime(__DATE__, __TIME__));
lcd.begin(16, 2);
lcd.setBacklight(HIGH); //HIGH is ON, LOW is OFF
}

26. TIMESET.INO, 2 OF 2
void loop()
{
now = RTC.now();
lcd.setCursor(0, 0);
lcd.print(now.year(), DEC);
lcd.print('/');
if(now.month() < 10) lcd.print("0");
lcd.print(now.month(), DEC);
lcd.print('/');
if(now.day() < 10) lcd.print("0");
lcd.print(now.day(), DEC);
lcd.setCursor(0, 1);
if(now.hour() < 10) lcd.print("0");
lcd.print(now.hour(), DEC);
lcd.print(':');
if(now.minute() < 10) lcd.print("0");
lcd.print(now.minute(), DEC);
lcd.print(':');
if(now.second() < 10) lcd.print("0");
lcd.print(now.second(), DEC);
delay(2000);
}

27. AUGUST 11, 2012 STORM IN PHOENIX
 About 10 hours of plot
BMP_mmHg
719.60
719.40
719.20
719.00
718.80
718.60
718.40
718.20
0 100 200 300 400 500 600

28. 39 HOTEL FLOORS AT
LAS VEGAS FOUR SEASONS
 Stepped up the logging rate to once per
second
 Three round trips
706
704
702
700
698
696
694
692
-500 0 500 1000 1500 2000

29. FUTURE WORK
 Add time setting over serial while running
 Seems to be a small temperature rise of
about 2 degrees F with the display running
 Add fancier display, perhaps a 1 hour plot of
data on a dot matrix display

30. DCC_DATALOGGER_3.INO 1 OF 9
// DCC_DataLogger.ino
#include <Wire.h>
#include <RTClib.h>
#include <Adafruit_BMP085.h>
#include <LiquidCrystal.h>
#include <SD.h>
// On display, connect via i2c, default address #0 (A0-A2 not jumpered)
LiquidCrystal lcd(0);
RTC_DS1307 RTC;
Adafruit_BMP085 bmp;
const int chipSelect = 10;
File dataFile;
unsigned long int press; // press is a long
float tempy; // temperature is a float
float fpress;
int loopSec = 0;
int loopMin = 0;
int num;
// make a string for assembling the data to log:
String dataString = "";
DateTime now;

31. DCC_DATALOGGER_3.INO 2 OF 9
void setup()
{
Serial.begin(57600);
Wire.begin();
RTC.begin();
bmp.begin();
// set up the LCD's number of rows and columns:
lcd.begin(16, 2);
lcd.setBacklight(HIGH); //HIGH is ON, LOW is OFF
if (! RTC.isrunning())
{
Serial.println("RTC is NOT running!");
// following line sets the RTC to the date & time this sketch was compiled
RTC.adjust(DateTime(__DATE__, __TIME__));
}
Serial.print("Initializing SD card...");
// make sure that the default chip select pin is set to
// output, even if you don't use it:
pinMode(SS, OUTPUT);

32. DCC_DATALOGGER_3.INO 3 OF 9
// see if the card is present and can be initialized:
if (!SD.begin(chipSelect))
{
Serial.println("Card failed, or not present");
// don't do anything more:
while (1) ;
}
Serial.println("card initialized.");
// Open up the file we're going to log to!
// This is an APPEND open
dataFile = SD.open("datalog.txt", FILE_WRITE);
if (! dataFile)
{
Serial.println("error opening datalog.txt");
// Wait forever since we can't write data
while (1) ;
}
}

33. DCC_DATALOGGER_3.INO 4 OF 9
void loop()
{
static int i;
if ( (loopSec % 5) == 0)
{
//Serial.println(__DATE__, __TIME__);
tempy = bmp.readTemperature();
tempy = (tempy * 9.0 / 5.0) + 32.0;
press = bmp.readPressure();
fpress = (float)press* 0.007500616827042;
now = RTC.now();
Serial.print(now.year(), DEC);
Serial.print('/');
if(now.month() < 10) Serial.print("0");
Serial.print(now.month(), DEC);
Serial.print('/');
if(now.day() < 10) Serial.print("0");
Serial.print(now.day(), DEC);
Serial.print(' ');

34. DCC_DATALOGGER_3.INO 5 OF 9
if(now.hour() < 10) Serial.print("0");
Serial.print(now.hour(), DEC);
Serial.print(':');
if(now.minute() < 10) Serial.print("0");
Serial.print(now.minute(), DEC);
Serial.print(':');
if(now.second() < 10) Serial.print("0");
Serial.print(now.second(), DEC);
Serial.println();
Serial.print("C time is = ");
Serial.println(now.unixtime());
lcd.setCursor(0, 0);
// lcd.print(now.year(), DEC);
// lcd.print('/');
if(now.month() < 10) lcd.print("0");
lcd.print(now.month(), DEC);
lcd.print('/');
if(now.day() < 10) lcd.print("0");
lcd.print(now.day(), DEC);
lcd.print(" ");

35. DCC_DATALOGGER_3.INO 6 OF 9
if(now.hour() < 10) lcd.print("0");
lcd.print(now.hour(), DEC);
lcd.print(':');
if(now.minute() < 10) lcd.print("0");
lcd.print(now.minute(), DEC);
lcd.print(':');
if(now.second() < 10) lcd.print("0");
lcd.print(now.second(), DEC);
lcd.setCursor(0, 1);
lcd.print(tempy,1);
lcd.print("F");
lcd.print(" ");
lcd.print(fpress,1);
lcd.print("mmHg");
Serial.print(tempy,1);
Serial.print(" Deg F, ");
Serial.print(fpress,1);
Serial.println(" mmHgn");
}

36. DCC_DATALOGGER_3.INO 7 OF 9
delay(1000);
loopSec+=1;
if(loopSec == 360) // 6 minutes
{
static bool lcdStatus = true; // LCD light on or off
loopSec = 0;
lcd.clear();
lcd.setCursor(0, 0);
lcd.print("Writing SD...");
dataString = String(now.unixtime());
dataString += ",";
num = tempy;
dataString += String(num);
dataString += ".";
tempy-=num;
tempy+=0.05;
tempy*=10.0;
num=tempy;
dataString+=String(num);
dataString += ",";
num = fpress;
dataString += String(num);

37. DCC_DATALOGGER_3.INO 8 OF 9
dataString += ".";
fpress-=num;
fpress+=0.05;
fpress*=10.0;
num = tempy;
dataString +=String(num);
dataFile.println(dataString);
// The following line will 'save' the file to the SD card after every
// line of data - this will use more power and slow down how much data
// you can read but it's safer!
// If you want to speed up the system, remove the call to flush() and it
// will save the file only every 512 bytes - every time a sector on the
// SD card is filled with data.
dataFile.flush();
delay(1000);
lcd.clear();
// To check out if display LED was causing warming,
// cycle it off/on every six minutes
// #define LEDONOFF
#ifdef LEDONOFF
lcdStatus = !lcdStatus;

38. DCC_DATALOGGER_3.INO 9 OF 9
if(lcdStatus)
{
lcd.setBacklight(HIGH); //HIGH is ON, LOW is OFF
}
else
{
lcd.setBacklight(LOW); //HIGH is ON, LOW is OFF
}
#endif
}
}

39. DOWNLOADS 1
 Grateful to Lady Ada!!!!
 Adafruit SD library:
https://github.com/adafruit/SD
 Adafruit RTC library:
https://github.com/adafruit/RTClib
 Adafruit logging shield tutorial:
http://learn.adafruit.com/adafruit-data-logger-
shield

40. DOWNLOADS 2
 LCD i2c backpack tutorial
 http://learn.adafruit.com/i2c-spi-lcd-backpack
 Liquid Crystal control library
 https://github.com/adafruit/LiquidCrystal

41. QUESTIONS?
 Find more slides from Don at
www.slideshare.net/dondoerres