![\"graph.png\"](\"https:\/\/tigoe.com\/pcomp\/code\/wp-content\/uploads\/2008\/01\/graph.png\")
<\/p>\nI’ve been looking for simple ways to graph the data from a sensor attached to a microcontroller lately, because it’s such a necessary activity if you want to look at sensor data over time. Using Apples Grapher program, which comes with OSX, I found a simple way that involves only four lines of code on an Arduino or Wiring microcontroller, and produces graphs like this:<\/p>\n
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Grapher lets you import text files with data point values. So here’s the procedure:<\/p>\n
\n1. Program the microcontroller<\/strong> Here’s the code for a Wiring or Arduino microcontroller. It prints the time in 100ths of a second, and the sensor reading at that time:<\/p>\n Note that the last line is a println(). That makes sure that each sensor reading gets its own line.2. Use screen to save the values<\/strong> \nNow open the screen program by typing:<\/p>\n \nwhere serialportname is the name of your serial port. For example, a typical Arduino module (or FTDI USB-to-serial adaptor) might show up as \/dev\/tty.usb-A400133P. So you’d type screen -L \/dev\/tty.usb-A400133P<\/tt>. I’ve been looking for simple ways to graph the data from a sensor attached to a microcontroller lately, because it’s such a necessary activity if you want to look at sensor data over time. Using Apples Grapher program, which comes with OSX, I found a simple way that involves only four lines of code on … <\/p>\n\n\nvoid setup() {\n\t\/\/ initialize the serial port:\n\tSerial.begin(9600);\n}\n\nvoid loop() {\n\t\/\/ print the time, in 100ths of a second:\n\tSerial.print(millis()\/10);\n\t\/\/ print a comma:\n\tSerial.print(\",\");\n\t\/\/ print the sensor value (connected to analog pin 0):\n\tSerial.println(analogRead(0));\n}\n\n<\/pre>\n
\nThe screen program in OSX and other Unix and Linux operating systems is a command-line program that allows you to see data coming in the serial port. You can learn more about using it here. It can also save data to a file, using the -L option. To use it, open a Terminal window. Change directories to the Desktop by typing:<\/p>\n\ncd Desktop\n<\/pre>\n
\nscreen -L serialportname\n<\/pre>\n
\nAs you hit the enter key to start the screen program, hit the rest button on your microcontroller. This will reset the time. A few seconds later, data will flow across the screen. When you’ve got enough data, type control-C to stop it, then control-A<\/tt> followed by control-\<\/tt> to close the screen program.
\n3. Convert the file to a .csv file<\/strong>
\nIf you look on the Desktop, you’ll see a file called screenlog.0. Open it in a text editor and save it as a text-only file called screenlog.csv<\/tt>.
\n4. Graph the data<\/strong> Now open the Grapher application. It lives in the Applications\/Utilities directory. Open a new default graph. From the Equation menu, choose “New Point Set”. A few new points will appear on the screen:<\/p>\n![\"new_points.png\"](\"https:\/\/tigoe.com\/pcomp\/code\/wp-content\/uploads\/2008\/01\/new-points.png\")
Click “Edit Points” and you’ll get a list of the points and their values. Select all the points and delete them.<\/p>\n![\"select_points.png\"](\"https:\/\/tigoe.com\/pcomp\/code\/wp-content\/uploads\/2008\/01\/select-points.png\")
Then click “Import ” and import your screenlog.csv file. Zoom out until you see the data points, and that’s it! For two sensor values at a time, you can send three values and view the graph in the 3D view as well.<\/p>\n![\"graphed_points.png\"](\"https:\/\/tigoe.com\/pcomp\/code\/wp-content\/uploads\/2008\/01\/graphed-points.png\")
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