EXPECTED PROBLEMS

The team is currently using five PIR sensors to detect and track the presence of humans in a room. Initial testing has indicated that these sensors are highly dependent of the proximity of the human to the sensors. It was found that the sensors, including the amplification circuits, would saturate and become unstable if a person walked to close to the sensor apparatus.

In an effort to prevent and/or minimize the effect of these instabilities, the team is planning on implementing two major changes to the existing designs. The first step will be to make the amplifier circuits have variable gain such that the sensors can be optimized to work at different sensitivities. ‘Blinders’ will also be installed on each PIR sensor to limit its field of view and therefore its total radiation exposure. Adding blinders may also simplify the intelligence algorithm because there will be little overlap between the field of view of each sensor.

The current system uses a small stepper motor attached to a turntable via a set of pulleys that are connected by a single strand of twine. This interconnection method allows for some flexibility and slip in the motor/turntable operation. To solve this problem, the team will replace the existing twine interconnection material with a more robust material similar to what is used in the automotive industry.

Accuracy errors can occur with the stepper motor. The motor uses a method of counting pulses on the output of the microcontroller. It is possible that some steps may be missed by the motor. This causes the turntable to be off-set proportional to the amount of missed pulses. To reduce the effect of these inaccuracies and to increase the reliability and repeatability of the control system, the team will consider implementing a feedback control scheme. The feedback control system incorporates a collocated potentiometer directly attached to the turntable axis. This allows system to exactly measure the position of the turntable. The team will test the design in the prototyping stage and determine if a potentiometer is necessary.

Due to the nature of the sensors that are being used in this design, a powerful processor with fast analog to digital conversion is required. Also, analysis of up to six analog channels is required to determine to position and movement of humans in the TV’s field of view. These requirements indicate that the microprocessor must have enough memory and fast enough clock speed to read, store, and analyze potentially thousands of readings per second.

The team has selected a microcontroller that is very efficient, fast, and has a large memory area. This alone does not guarantee a successful completion of this project. The team must also develop an equally efficient and fast algorithm to analyze this data while trying to keep the memory usage to a minimum.