Shown here is a block diagram of a single phase Brushless DC Motor control sample circuit. The features of the PWM module allows the micro to control the speed of the motor and the Hall IC, through the comparators, allow the control loop software running on the processor to determine the speed of the motor. The ML610Q100 series devices have analog comparators which are used to monitor analog outputs from Hall Effect elements, which are less expensive than digital output Hall Effect Sensors. Hall effect elements and sensors detect magnetic fields. A small magnet is embedded in the rotating portion of the fan and the hall element is placed close to the rotating part of the fan, so that it’s output can be used to determine the rotational speed of the fan. Monitoring the hall element provides feedback to the controller so that it can determine if the fan is at the desired speed and adjust the PWM settings accordingly. The comparators on these devices have been optimized to be accurate over wide operating voltage and temperature ranges and include differential input and hysteresis, which all simplify and enable the use of a relatively inexpensive Hall Effect element. The timers, PWM module, and comparator can be used to create a closed loop system that smoothly starts, controls the speed, and stops a fan motor. Example programs that show this application are available online.