In the meanwhile I build the DelTang transmitter in combination with the channel multiplexer as given from DelTang for switching the joints and tested it. The result is not really good. The relais rattled while pressing the key on the transmitter. That was not, what I was looking for.
So I started searching the internet again for other solutions and found a WIFI controlled relay boards. If you are interrested for further information, please search for “Aptinex IOT 4 channel relay module”. I found it on eBay for less than 20 Euros including shipping. Each board contains a micro WIFI webserver, but it is also possible to send get/post command to the board. It is possible to control two joints with one board (J1 left, J1 right, J2 left, J2 right). It is also possible to change the IP address. So it is possible to use several of them.
As I have a constant supply power on my tracks, I just need to take the power of the tracks, bring it to 5 volts DC for the power supply and may place the receivers locally next to the joints.
I plan to place the board into a waterproof box, having 3 cables getting out of it. One for each joint and one for the power supply.
I’m awaiting the boards and give you feedback as soon as I have tested them…..