I assembled the circuit as planned, but it seems the values are wrong.... apparently the inversion is making problems there. I tried to send values as strings for the test, but instead of "11.1" I am receiving values like 6x[-
Would check in the evening, if the too high resistor value affects that. If not, will try to hang the opto in normal off, between pin and +5V then... (by shifting the GND wire to signal, and Signal wire to +5 of arduino)