Low-Cost Passive IR Sensing with RS08KA

This document describes how to implement a passive infrared (PIR) motion detector using Freescale's low-cost RS08KA microcontroller family. The base function of this design is to switch on appliances, especially lighting, in response to movement. The main idea behind this solution is to replace the common analog motion detector with an ultra low-cost digital design, based on the MC9RS08KA1. The most important part of this document consists of the detection algorithm and the method for measuring the analog signal from the PIR sensor. This document focuses on a software sigma-delta analog-todigital conversion method, and shows in detail all parts of the hardware and software implementation of a passive infrared (PIR) detector. The main feature of this document is a demonstration of the capabilities of the low-cost RS08KA series of MCUs. It also shows fully functional and practical implementation and use of ultra-low-cost microcontrollers, but does not include some necessary peripherals for measuring and creating complex solutions using PIR sensing. All schematics, board layout, and complete software pack are available on freescale.com. Features include: • Design of low-cost PIR motion detector based on HC9RS08KA MCU Freescale Semiconductor Document Number: AN4305 Application Note Rev. 0, August 2011