Now there are two ways to switch the joints of my garden railway:
1) Raspberry Pi website
2) my brand new controller device
The controller device contains a nodeMCU V3 (contains a ESP8266-12) and a 16ch Multiplexer breakout board. Using this combination, it is possible to connect (at least) 16 electrical switches to the nodeMCU. I implemented the related code under the Arduino environment for the nodeMCU board a few weeks ago. Today I assembled the hardware components to a ready-to-use device. The USB port at the backside is for charging the 5VDC powerpack, which supplies the nodeMCU.