good morning,
That s a nice project you get there, and the description document is very well made. i have worked recently with a customer on a similaire issue, signal rising edge detection and counting time between edges, then ring an alarm when there is no rising edge for a certain time. in your case it is a motor shaft with hall effect sensor along with the details of the project.
I can make it for you.
here is what i purpose, you don't pay nothing, until you see it work, i test all my arduino codes before i send them to clients, i have a the minimum material needed for the tests : Uno, LDC, keypad, push buttons and some sensors. Code will be commented, professionally made, and easy to modify for future adjustment if needed.
Best Regards.