Thanks for all the help so far guys, but at the moment I'm a bit confused:
This is the original circuit :
So now I wanted to measure the current so I added the resistor and read the voltage value with the arduino analog input like so :
OK, that works nicely, But, now I also want to measure the voltage over the led : But obviously I can't just add another ground before the led and a an arduino pin after the led. So do I just set GND to starting ground and then read voltages at the different points with multiple analog inputs ? :
does that make sense ? Will my 'current measure resistor' still do its job that way?
Thanks again for all the help