Arduino hall Effect Sensor project

Project components:
-Hall effect sensor
-magnet
-lenoardo board connected to pc
-push button

Will install of a magnet on a rotating wheel, and a fixed hall effect sensor
when the magnet move in front of the sensor, i need the leonardo board to send to pc keyboard stroke letter "A"
when the push button is pressed, leonardo board to send keyboard stroke letter "B"

i want to control when board sends letter A to pc,
ex: for each 3 moves of the magnet in front of the sensor, send one time keyboard stroke letter "A" and repeat for the next 3 moves and so on
i need to control the variable in the code manually