Human Detection Sensor System

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 distance measuring device.

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 left. 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.

• Pyroelectric Infrared Sensor
• LP324N Op-Amp

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).