1. Introduction
This application note describes how to implement a brushless DC motor control in
sensor mode using the ATmega32M1 AVR microcontroller.
The high performance AVR core fitted with Power Stage Controller module of
ATmega32M1 allows to design high speed brushless DC motor applications.
In this document, we will give a short description of brushless DC motor theory of
operations, we will detail how to control a brushless DC motor in sensor mode and we
will also give a short description of the ATAVRMC310 and ATAVRMC300 boards
used in this application note.
Software implementation is also discussed with software control loop using a PID
filter.
This application note deals only with BLDC motor control application using Hall effect
position sensors to control commutation sequence.
2. Theory of Operation
Brushless DC motors are used in a growing number of motor applications as they
have many advantages:
They have no brushes so they require little or no maintenance.
They generate less acoustic and electrical noise than universal brushed DC motors.
They can be used in hazardous operation environments (with flammable products).
8-bit
Microcontroller
Application Note
8138A–AVR–04/08
8138A–AVR–04/08
AVR194
They also have a good weight/size to power ratio.
Such motors have little rotor inertia. The coils are attached to the stator. The commutation is
controlled by electronics. Commutation times are provided either by position sensors or by coils
Back Electromotive Force measurements.
In sensor mode, Brushless DC motors usually consist of three main parts: a Stator, a Rotor and
Hall Sensors.
2.1 Stator
A basic three phases BLDC motor Stator has three coils. In many motors the number of coils is
replicated to have a smaller torque ripple.
Figure 1 shows the electrical schematic of the stator. It consists of three coils each including
three elements in series, an inductance, a resistance and one back electromotive force.

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