SerialPort is a library from Bill Greiman’s beta library.

OpenLog currently uses the 20120106 version.

Unzip ‘SerialPortBeta20120106.zip’ and ‘SdFatBeta20120108.zip’ to Arduino’s “libraries” directory (usually something like C:\arduino-1.0\libraries) and close and restart Arduino. To verify these are installed correctly, you should now see ‘SerialPort’ and ‘SdFat’ under the File->Examples menu.

For more information about installing Arduino libraries see the SparkFun Learn tutorial.