this project is intended to make a circuit for detect when the motor shaft comes to a halt,here a small contactor attached to the shaft of the motor. As the motor rotates this contactor touches two pins A and B there by giving pulse to the comparator through a trigger circuit. As soon as the connection is established the output of the comparator changes and remains at that state for some time say for 0.25 seconds, before the output can change back, the contactor touches the pins again and again triggers the comparator. This continues as long as the shaft is moving.But the moment the shaft stops, the comparator no-longer gets any pulse for 0.25 seconds and it changes state, hence get to know that the motor has stopped rotating.The reason why need the trigger circuit is that Even if the shaft comes to halt exactly at the point where it touches pin A and B, the comparator receives only one trigger through the trigger circuit and does not get second trigger for 0.25 seconds.



http://freepatentsonline2877456.pdf
http://forum.allaboutcircuitsshowthread.php?t=26749