Measuring current or voltage drop over the motors can works, but it
changes so much from different brands, contacts resistances and so one,
even some extra drags on the windows can sometimes reach the same
current of the end-of-curse.

Actually when the motor reaches the end-of-curse position, it (most of
the times) enter in a steady condition of non movement, with a (almost)
constant current or voltage drop, so monitoring this situation could be
a solution.

If you could install something close to the motor, a field effect sensor
would be (probably) a solution, since the magnetic field around the
motor is changing when the motor is rotating, and somehow steady when it
is overload and blocked.

If you really can install things, do what all the manufacturers should
do long ago, install limit switches...!

--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm