EDIT:
i didn t try with the debouncing in the isr because i like to take it "as short as possible"
so i used the capacitator:
rpmcount: 0 | sensor: 1 | rpm: 0
rpmcount: 0 | sensor: 1 | rpm: 0
rpmcount: 0 | sensor: 1 | rpm: 0
rpmcount: 0 | sensor: 0 | rpm: 0
rpmcount: 1 | sensor: 0 | rpm: 0
rpmcount: 1 | sensor: 0 | rpm: 0
rpmcount: 1 | sensor: 0 | rpm: 0
rpmcount: 1 | sensor: 0 | rpm: 0
rpmcount: 1 | sensor: 1 | rpm: 0
rpmcount: 1 | sensor: 1 | rpm: 0
rpmcount: 1 | sensor: 1 | rpm: 0
pmcount: 1 | sensor: 1 | rpm: 0
rpmcount: 1 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 2 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 1 | rpm: 0
rpmcount: 2 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 0 | rpm: 0
rpmcount: 3 | sensor: 1 | rpm: 0
rpmcount: 3 | sensor: 1 | rpm: 0
rpmcount: 3 | sensor: 1 | rpm: 0
rpmcount: 13 | sensor: 1 | rpm: 0
rpmcount: 13 | sensor: 1 | rpm: 0
rpmcount: 13 | sensor: 1 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 0 | rpm: 0
rpmcount: 14 | sensor: 1 | rpm: 0
rpmcount: 14 | sensor: 1 | rpm: 0
rpmcount: 14 | sensor: 1 | rpm: 0
my thanks and complimets to everyone expecially cattledog
i tried it with a fan and looks good, in the next days i will try with the brushless motors hoping it will be enough fast for them
i also tried to put the INPUT_PULLUP in my interrept but it looks like that works worst (but i could be just a mine impression)