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Since the PIR sensor is a passive device, it only receives light. An optical filter allows transmission of infrared light with wavelengths greater than 5 µm. For a frame of reference, a human body typically emits a wavelength of around 10 µm. After the infrared light passes through the filter, it is absorbed by the pyroelectric elements. The Panasonic sensor contains four elements which are each polarized to create positive and negative detection zones. As an element becomes saturated, it converts the light into a small positive or negative analog voltage signal. Since this voltage is very small, an integrated circuit inside the sensor is used to amplify the signal. The sensors then take this amplified analog signal and convert it to a digital signal by using a preset threshold voltage programmed inside the ASIC. As the analog voltage goes above the positive or negative threshold values, a digital signal passes through the output of the sensor.
