The here shown C64 User-Port Expander is a recreation of the Scanntronik Userportweiche from 1990.
This Expander extends the C64 with 2 additional User-Port slots. The electronic logic switches automatically between the connected devices. The circuit contains a driver IC to protect the C64 from overstressing its port IC and to provide enough power to connect long cables. One slot is especially dedicated to connect a printer.
Last Update: 18.02.2019 
C64 Userport Expander
The original and the rebuild.
Boards in the making.
The circuit
The new design which contains the three separate parts of the board.
Expander build up.