Pins 7 to 40 should be used for the clock LEDs.

Pins 1 to 6 are free for optional I²C devices and other GPIO stuff.

Default Pinout:

Note: The LED to GPIO mapping can be easily changed in source code

See detail description on https://github.com/fablab-wue/piClock/blob/master/prepare.md

In short:

• Setup network/WiFi
• Disable SPI, 1-Wire, Serial
• Install Python3, pigpio-lib
• Download source from GitHub
• Autostart at boot the ~/piClock/franconian.py

Linux experts will configure the RPi in no-time. Less experienced users (like me) needed more time for configuring than for wood-working and soldering.