Thanks for the quick reply
I do own a (cheap) multimeter.. I also thought about debugging it that way, but all I can get out of it is what I wrote above. NQ shows a voltage of +4-5V and Q is around 0.2V
There's a line running from +5V over a 1k resistor to Gnd. Before that resistor I added the wire going to D.
So, using the multimeter, I can confirm that D is HIGH, S is LOW and R is LOW too.
The only thing that bothers me now is the edge triggering. I already tried pulling the Clk line out before powering the circuit and then plugging it in. The thing is, I need to control the flip flops (both, D and Clk) from a simple pushbutton, while the reset afterwards comes from the arduino. The arduino will globally reset all flip flops on the circuit (there's around 6 of them, so 12 flip flops overall)
Pins are definitely connected correctly. Only thing that could be wrong is the wiring of Vdd and Vss. Vdd runs from +5V and Vss runs to Gnd.
What's also interesting is that if I completely remove the LED and the resistor leading to it from Q, I get 0V on Q and +4-5V on NQ. The LED lights up on NQ.
However, if I add the LED and resistor to Q, I get 0V on NQ and +4-5V on Q, however, the LED doesn't turn on.. that somehow seems illogical..
I'm testing with the multimeter from the wire leading to Vdd and the Q/NQ pins.
Also, another observation:
Setting the third pin (Clk1) HIGH gives me +5V on Q and 0V on NQ, while D is either floating or connected to Gnd. Afterwards, setting it to LOW leaves +5V on Q and 0V on NQ, which obviously shouldn't happen since D is always LOW. This way, when Clk1 becomes LOW, Q should also become LOW and not stay HIGH. Like I said, it can't be wired wrong, it's the third pin, which is Clk1.
Also, setting R to HIGH should give me 0V on Q and +5V on NQ, which it doesn't. Even when Clk1 and D are LOW.