Most cars produced now with motorized windows use a current sensing scheme like
what you mention here.  There are specialized chips for doing this, as well as
precision shunts for current sensing.

This was covered awhile ago, search the piclist archives for current sensing, or
car windows.

-Adam

Sebastian Garcia wrote:
>
> Hi all!
>
> In this (car alarm expansion module...)project, when a trigger occurs the
> system switchs on the electric glasses motors, and then I need to sense when
> the glasses are full up, to turn off the motors.
>
> To sense this window closing without using any external sensors and wires, I
> though in sensing the dc motor current; when the glass get full high the
> current will increase and the uC can detect it and turn off the motor.
> Maybe sensing the voltage drop on a low value series (power...) resistor, or
> sensing the change of current (and magnetic flux) when the motor stops, with
> an external coil (provided with ferromagnetic core...) A PIC with ADC can
> then do the remaining job.
>
> I know, there are security issues involved in this kind of approach (Hand
> pushing the glass when closing...)
>
> Any better approach? Any hints?
>
> I'm trying to avoid the use of, for example, piezo sensors, because of the
> problem of the wires and external mounting.
>
> TIA,
>
> S.-
>
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