ECE 4760: Final Projects

Smart Fan

A Human Tracking Fan System

Joseph Fridlander (

Emmeline Park (

"a human tracking rotating platform that supports a fan"

project soundbyte

For our final project we decided to construct a human tracking rotating platform that supports a fan.

The platform, using dual element Pyroelectric Infrared Sensors (PIR) sensors, rotates itself independently to direct air flow to whatever position a person moves to. In addition, the fan includes another setting that allows precise rotation between two people. These modes are selectable by the user. The running mode is displayed on an LCD.

We decided to pursue this project because we had become fed up with the common fan’s limitations.

3. The Pyroelectric Infrared Sensor Circuits

A standard circuit application was used to detect a person. The schematic can be seen below. It was modified to serve our project purposes. The PIR sensor can be modeled as a BJT. When the device is triggered current flows through the BJT and a signal voltage proportional to the amount of current is produced. The circuit biases the sensor output and integrates it. The output of the integrator is fed into the comparator which we adjusted to obtain the best sensitivity we thought made the system operate best. When the output is greater than the threshold the output goes from low to high.


PIR Circuit

Upon detection, the output of the comparator remains high for as much as 2.5 seconds. This degrades system performance for reasons that are explained later. To fix this we increased the comparator threshold as well as decreased the feedback resistor on the integrator. Although both solutions improved the response of the circuit these solutions decreased the sensor’s range. Thus, we decided to minimize these changes as much as possible.

4. Limit Sensors

To avoid hazardous situations such as tangled wires the fan was allowed to rotate at angles that were no greater than 180 degrees. Two metal strips, one on each side of the fan, were grounded. Another strip of metal was mounted on the lazy Susan at the front center of the platform. The lazy Susan was connected to a pin on the development board with an activated pull up resistor. When the strips of metal touched, the pin was set low and detected by the microcontroller. The software was set to check the sensor every 50 msec. The sensors can be seen in Figure 3.


Figure 3a: Limit Sensors


Figure 3b: Limit Sensors