The human detection sensor system consists of a variety of sensors oriented in such a way that they can be used to detect and track the presence of humans. In our current design, there are three types of sensors: PIR Motion Detectors, Infrared Thermometer Arrays, and an ultrasonic range finder.

These sensors are comprised of a Pyroelectric Infrared Sensor along with a custom designed amplifier circuit. A datasheet for the Pyroelectric Sensor can be found below. Due to the complexity of the amplifier circuit, the team decided to print PCB's for these boards - an attempt to save time and effort.

The Pyro-Sensors is used to detect the movement of humans (or any heated body) in a defined field of view. These sensors work by using two active elements to detect relative direction of motion of a heated body. When an object moves in the sensors field of view, a voltage waveform is produced. An example waveform can be seen to the right. Each sensor has about 90 degrees viewing angle but, with the help of a Fresnel lens and blinders, the final setup will consist of four sensors each with 45 degree viewing angle.

The output from the Pyro-Sensors cannot be read directly into the microcontroller, so the team has constructed an amplification circuit capable of amplifying the signal with a variable-gain of over 10,000 (80dB). The amplifier is a simple two-stage Op-Amp circuit using the LM324 series Op-Amps. The amplifier circuit can be seen in the gallery below.

The TPA81 has an array of eight thermopiles arranged in a row. They can measure and report the absolute temperature of 8 adjacent points simultaneously as well as the ambient room temperature. The eight points are measured at increments of 5 rotational degrees. This gives the sensor an effective field of view of 8×5 = 40 degrees.

The thermopile array is attached to a rotating servo such that the sensor can detect objects around the entire 180 degree field of view. A simple program utilized this arrangement to track a single object moving in a room. The final design will utilize this sensor to get an accurate location of the moving human(s).

The thermopile array uses the I²C interface to communicate with the microcontroller.

The SRF10 range finder uses ultra-sonic waves to measure the distance of solid objects. Similar to an echo in a canyon, the range finder measures the time delay between the “ping” and the echo and then uses the delay to calculate the distance in cm. The range finder can detect object withing about a 90 degree viewing angle. Thus it is important that the ping sensor be mounted such that is can rotate to face viewers in all locations.

Similar to the thermopile array, the range finder is mounted to a rotating servo which allow rotation along the z-axis. This allows one range finder to cover the entire 180 degree field of view.

The SRF10 uses the I²C interface to communicate with the microcontroller.

• Code for relaying four PIR sensor data to the PC via the serial port
• Code for relaying one PIR sensor data to the PC via the serial port
• Code to read raw data from the TPA81 sensor to the console