This little extension board provides the Elektor Linuxboard with a single real time clock. The Elektor extension board for the Elektor Linuxboard has a real time clock and a display and additional I/O. If only a real time clock is needed this little extension is sufficient. It uses a DS1337. The chip has two output pins for alarms that can be configured in software. The second alarm output pin can be configured as a programmable square wave output. The extension is supplied by the Elektor Linuxboard with 3,3V DC. A battery provides supply to the chip during power down.