I got the oscilloscope of the physics department to run some tests on the circuit board and the results are great.
The signal on the oscilloscope definitely shows the characteristics of the photodiode from the Opto-isolator, but that was no problem for our test equipment, it lights up again.
Since the summer holidays begin in the next day, we finished with the prototype of the hardware and went over to the software side. Hopefully the software will have a lot more features to test at the end of the summer break.
With great regards, Langhalsdino