The SF series of diaries have a serial communications port which can be used to connect to other diaries or to a computer with a suitable interface cable and software. The contents of the diary can be uploaded for backup purposes and/or modified on the computer for subsequent down-loading.
The SF serial communications port runs at logic levels of circa 4 or 5 volts. These need to be converted to normal RS-232 serial port levels which can be achieved using common integrated circuits such as the MAX232 from Maxim. You can either buy a ready made cable or build your own. The latter option isn't too difficult provided you have made some electronics projects before.
Personally, I prefer any circuit using the MAX devices particularly because they are fully compliant with RS-232 standards.
NB Victor Wiewiórowski also has an excellent software page.
