karlok:
maybe with some kind of digitalRead and two wires attached after the diodes? Any idea to do this?
Remember, you don't want to attach these voltage levels directly to any Arduino I/O pins, they will be at least 1 volt over 5 VDC those pins are made for. What you could do is have each pass through the input side of an opto-isolator (also called an opto-coupler) with the photo-transistor powered by the +5V pin from your Arduino. The photo-transistor in the two opto-isolators can be biased to work as a switch and can safely be wired to an I/O (you'll need one per opto-isolator).