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Stall detection of stepper motor during vibrating conditions using L9942

Question asked by Siva Murugesan on Sep 1, 2015
Hello Experts,

I am using a bipolar stepper motor and L9942 driver IC.
I am unable to set the stall threshold time for my application. 
The stall position to be identified is the end position of the linear actuator.
My application is to identify the stall, change direction of rotation and stop rotation after n number of step pulses.
I am able to arrive at a certain threshold value above which, the ST pin is set to 'logic high' immediately, even before the motor starting to spin (even if there is no stall condition)- so as per the logic the direction is changed and the motor rotates in the opposite direction, but the stall bit is not reset.
Below the same threshold value, the ST pin always remains low- even after stall conditions the ST pin remains low.
I am not able to arrive at that threshold value at which the driver detects proper stall condition.

Please refer to the following link. 
Back-EMF method detects stepper-motor stall

The link says that "A stalled but vibrating rotor shows an issue with BEMF detection".
In my application also the motor vibrates during stall condition, is this a reason for the Stall Bit not being set at proper stall conditons?

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