Quote:
Originally Posted by flores
I guess the current is to small to measure.. then the controller will automatically increase the duty cycle
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You might consider using one of the current sensors from Device Tech. They sell the small current sensors on FleaBay for under $10, shipping included.
They have a round 1/4" aperture, which is appropriate for their measurement rating. If you have a low current motor and need more measurement sensitivity you can loop the wire through the toroid a few times.
They run on 4.5-6.0V with the same centered ratiometric output of the LEM sensor. Ratiometric means that the output scales with the supply voltage: with a 5.00V supply the no-current output is 2.50V, with a 4.80V supply the output is 2.40V. This exactly what you want if the reference voltage for the A/D converter is the same as the supply voltage.
One aspect that is nicer than the LEM sensors is their lower power draw, with a disable input that puts the sensor in a micro-power off mode.