Im trying to understand how the Arduino ISR keeps track of timing between pulses stored in a variable, if that variable is latter used.
Say, for example, you have a magnet mounted on a circular object, that passes a reed switch. Using this to trigger the ISR that calls a function that would have something like counts++ in it, then storing that value in a variable.
If that varible is used latter to turn on a motor, for example, according to the count capture, how does the arduino MCU know the freq or timing to output the count or pulses of the magnet passing the reed switch, at the same frequency that the counts were received? For example, a magnet mounted on a 2 inch dia shaft would turn slower past a reed switch than one mounted on a .5 inch shaft, or one could vary the speed of the magnet past the reed as they wish. So how does counter++ keep track of this freq? is it reading the attachinterupt pin (or is the function that is being called, keeping track) or does the ISR time stamp each pulse it receives and store that interval in the declared variable? so when the variable is used again, it has this interval stored in it?
To be more clear, if it takes one second for the magnet to complete one revolution, how does the MCU know it took one second and store this, along with the counts of the revolutions?
Thanks for any help