Book Analog Interfacing to Embedded Microprocessors
When using the sensorless technique with a microprocessor, you will find
that there are noise spikes on the sensed coil when the transistors switch on
and off. You can filter this out with capacitors on the sense line, as shown in
Figure 7.26, or you can just ignore the samples from the sensed winding
during this interval.
There are a number of brushless DC motor drivers that can take advan-
tage of sensorless, EMF-based position sensing. The Philips TDA5140 will
drive motors up to about 8A and can use either a sensor or sensorless driving.
Encoders
PMDC and brushless DC motors are usually used in embedded systems with
an encoder attached to the shaft. This provides feedback to the micro-
processor as to motor position. A typical encoder is shown in Figure 7.27. In
this scheme, four magnets are placed around the shaft of the motor and a
Hall effect sensor is placed on the case. The Hall effect sensor will produce
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