ST7FLITE05/09/SUPERLITE low-cost PIR sensor design document
The document describes a method for creating a PIR detector by utilizing software Sigma-Delta A/D conversion techniques on the ST7LiteO5/09/Superlite microcontroller family. This approach is suitable for detecting low-frequency sensor signals generated by human movement, which radiates infrared waves between 8 and 12 micrometers.
The design uses a transistor circuit biased by the microcontroller to amplify the signal from the PIR sensor, replacing conventional Op-Amp based amplifiers to reduce costs. The system includes features such as tampering detection via a mechanical switch, hardware self-testing routines, and configurable sensitivity levels through software parameters.
| Infrared Wavelength Range | 8 to 12 micrometers |
|---|---|
| Detection Distance (Unfocused) | up to 10 inches |
The design supports the ST7FLITE05(09) and Superlite microcontroller families.
Sensitivity can be changed by assigning high or small values to parameters in the 'select_sensitivity()' function within main.c.
The test checks the status of transistor Q1 collector against the signal at the base of transistor Q3 upon power-on or reset.