"Paul Hovnanian P.E." wrote in message
...
Bill Noble wrote:

simple electronic way. Have a magnet on the rotating part. Place a reed
switch near enough that it closes every time the magnet comes by. Have a
timer you set to two seconds. Reset the timer when you presss "start",
and
every time the reed switch is closed by the magnet. You can make this
timer
from a 555 chip, or just buy a timer. If the timer expires, drop out a
relay to de-energize the motor.

That'll work until the output shaft stalls with the magnet over the reed
switch, holding the 555 timer in a reset state permanently.

Google "watchdog timer", or go to maxim-ic.com and search on that term.
There are one chip solutions that handle this (and other) gotchas.

--
Paul Hovnanian
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so, just capacitively couple to the reset pin - one part, no problem.