@Japio: I quit trying to get it working because some users are reporting sync issues with the arduino internal clock. I managed to get it work with a rs232 to ethernet adapter with a transistor used as inverter. I can connect in native tcp mode in domoticz to the ip adres of the adapter.
I tried to get te script working on a landis gyr e350 connected to an arduino mega. I have inverted the signal and connected it to pin 48 of the mega. The inverted signal shows up correctly if connect it directly to my laptops serial interface so that is working. I read that the DSMR4 protocol uses 115200/8/N/1 in stead of 9600/7/E/1. I cannot get the settings right for AltSoftSerial. Can someone help me modify the script to get the things working?