I have a rotating contact (contact breaker of an ICE) that switches between being not connected to anything (floating) and being connected to the case of the ICE. The engine case is connected to ground (same ground as the Arduino). Thus the signal is switching between short times of being on LOW (connected to ground) and mostly being floating. Both of these intervals are much higher than the usual hardware resolution for interrupts on the Arduino - think several microseconds of LOW vs some milliseconds of floating.
Since the "ON" state of the switch connects to ground, I was thinking that I could use the interrupt function of the Arduino to be informed whenever the state changes to LOW, to count how many times the engine rotates. However I have only seen this used in combination with a HIGH signal and not with a floating signal. I was wondering if this would also work and the interrupt would be triggered when the signal switches from floating to LOW.
What are my options to count a signal that switches between floating and the same ground signal as the Arduino?