Can I just plug one leg into +5V and the other into an analog pin? Or does something need to be connected to ground as well?
its resistance changes when light shines on it
Then change cathode pin to an input and using pulseIn see how long it takes to drop to a zero.
Will a 100ohm resistor make much difference compared to a 150 ohm
_SFR_IO8(0x35) |= 0x10; // global disable pull up resistors