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Datalogging with ArduinoPosted on 17 February 2012 by tigoe

There are several ways to save data from a sensor attached to an Arduino. If you’re

connected to a personal computer, y ou can simply send the data from the Arduino to the

personal computer serially, and save it to a file. If you’ve got an SD card attached to the

microcontroller, you can save the data to the card. Or, if you have access to the internet

and a device that can connect to a server, you can save the data to a server. In the tutorial

 below, you’ll read a DHT11 temperature and humidity sensor and log data in three ways:

Serial transmission to a personal computer, and serial capture to a file.

Saving data to an SD card mounted on the Arduino

HTTP upload to pachube.com via an Ethernet shield or Ethernet Arduino.

Hardware you need:

personal computer

Ethernet Arduino and USB-to-serial connector, or Arduino Uno and Ethernet shield (or

equivalents)

SD Micro card

DHT11 temperature and humidity sensor

10-kilohm resistor

Software you need:

 Arduino IDE 1.0 or later

 Adafruit DHT sensor library 

Datalogging examples from tigoe gitHub repository 

Spreadsheet; OpenOffice is used here, but Excel will work as well.

CoolTerm (optional)

 Account on pachube.com

Concepts you should know:

Basic understanding of Arduino code

Basic electrical concepts

Serial communication conceptsHow to install libraries in Arduino

HTTP request concepts

For more on the DHT sensors, see Adafruit’s tutorial.

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To get started, install the Arduino IDE and download the DHT library . Unzip the library 

and change the directory name to DHT, then copy it to the libraries/ directory of your

 Arduino sketch directory . If this is your first time using Arduino, the default location is in

 your user directory, called Arduino/ . You might have to create the libraries directory 

inside the sketch directory. Then download the example sketches from my gitHub

repository, unzip them and save them to your sketch directory as well. Then start the

 Arduino IDE.

Connecting the sensor

Connect the DHT1 1 sensor to the Arduino as follows:

 Vcc (pin 1) – Digital pin 8

Output (pin 2) – Digital pin 7

Ground (pin 4) – Digital pin 5

Since the DHT11 sensor uses very little current, you can use the output pins of the

microcontoller to power the sensor, using pins 5 and 8. Then attach the output pin of the

sensor to pin 7. The output pin will also need a pullup resistor so that it goes high when no

data is transmitted. To do this, connect the 10-kilohm resistor from pin 8 to pin 7, or to the

+5V pin.

Serial Data Capture to a Graph

The simplest way to get data off the sensor is to print the results out serially and capture

them directly on your computer. To make this happen, you’ll need your Arduino attached

 via a USB-to-serial connection. The sketch SerialTempHumidityReader uses the Adafruit

DHT library to read the sensor and sends the results back to the computer serially.

Download it and copy it into a new window in the Arduino IDE.

To upload the sketch to your board, connect the board to the computer via USB-to-serial,

and look for the board type in the Tools > Board menu. Assuming you’re using an Arduino

Ethernet, choose that:

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To find your serial port, check the Tools >Serial Port menu with the USB-to-serial adapter

NOT connected. Then plug the adapter into your computer again and check the menu

again. The new port that shows up is your USB-to-serial adapter’s port.

Once you’ve selected the board type and the port, upload the sketch by clicking the upload

 button in the toolbar, or ctrl-U:

 When you’ve got the sketch loaded, open the serial monitor by clicking the Serial Monitor button on the right hand side of the toolbar.

 You should see readings like this:

The sketch is outputting tab-separated data, and prints out column headers at the

 beginning.

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 When you’ve got several readings, click in the serial monitor window, select all (ctrl-A), and

copy (ctrl-C). Then open a blank spreadsheet in OpenOffice and paste the results into the

sheet. When the Text Import dialog comes up, make sure you click Separated by Tab in

the Separator options:

Select the two columns of numbers, and click the graph icon. In the Graph dialog box,

choose Line type, the Lines Only option, then click Finish. Your graph will be inserted in

 your spreadsheet. Voila, graphing made simple!

Serial Data Capture to a File

If y ou have a serial terminal program like CoolTerm on your computer, y ou can also

capture to a file. To do so, open CoolTerm, and choose your serial port in the Options

menu. Click the Connect icon, then from the Connection Menu, choose Capture to

TextFile… and Start. Give your file a name and save.

 Note: if you want the file to start from the beginning of your sketch, hold down the reset 

until you’ve started capture.

To stop capture, choose Connect > Capture to TextFile… > Stop. Then you can use your file

in any application you want. Change the file extension to .csv and you can open it in a

spreadsheet and graph as above.

Saving Data to an SD Card

Sometimes you want to save data when you’re not connected to a personal computer.

 Attaching an SD card to an Arduino is fairly straightforward. There are several different

shields that have SD cards on board, and the Arduino Ethernet has an SD card right on the

main board. The SD card library makes it simple to save files to y our SD card.

Format a microSD card as FAT16 or FAT32 on your personal computer, and load it onto

 your Arduino. Then upload the SDCardDataLogger  sketch. This sketch reads the sensor

using the Adafuit DHT library , and if there is an SD card present and initialized, it saves

the results to a file called “DATALOG.CSV”. Transfer this file to your computer and use it

as you wish. You can open it in a spreadsheet and graph it as y ou did above, or anything

else you wish.

Posting data to Pachube.com

If y our Arduino is connected to the internet via Ethernet, you can connect to pachube.comand program it to post data there. Then you can use Pachube’s data storage and graphing

tools to save and visualize your data.

Set up a pachube.com account. Click Create a Feed. Give it a name, add any descriptive

tags y ou want, and add a location if you wish. Add two datastreams called rH (relative

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humidity) and temp (temperature) as follows:

 Write down the feed number and fill it into the feed variable in the sketch

(PachubeDataLogger). You’ll also need your API key, which is a long string that identifies

 you to pachube.com. Click My Keys from the pachube menu to get your key. Copy it into

the apiKey variable in the sketch below.

Upload this sketch to your Arduino, and connect the board to the net v ia Ethernet. Open

the serial monitor. When the sketch starts, it will look for an IP address using DHCP. Then

every ten seconds, it will read the sensor and try to upload to Pachube. A successful upload

 will print out something like this:

192.168.2.6

rH,26.00

temp,30.00

connecting...

data uploaded

HTTP/1.1 200 OK

Date: Sat, 16 Feb 2012 10:03:14 GMT

Content-Type: text/plain; charset=utf-8

Connection: close

X-Pachube-Logging-Key: logging.G5DkQtnxEdwyKbk0KSKI

X-PachubeRequestId: 0b4efe30282b715276cf1f849f7123ed3eaba234

Cache-Control: max-age=0

Content-Length: 1

Age: 0

Vary: Accept-Encoding

 When you look at your feed, you’ll see a graph of your temperature and humidity.

Now you’ve got sev eral methods to log data from an Arduino. You can change the sensor to

any sensor you wish, and revise the sketches shown here to read that sensor instead of the

DHT11. Enjoy!

Update

I’ve added code to the repository for this tutorial that shows how to use the Pachube code

 with a BMP085 barometric pressure sensor. Thanks to Adafruit for the excellent library 

for this sensor. I’v e also added an example showing how to use the BMP085 with the SD

card, and with a Realtime Clock . Again, Adafruit’s library for the RTC makes this easy.

 

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