AN238 Datasheet | Microchip Technology

.. Tire Pressure Monitoring (TPM) System Authors: Ruan Lourens Microchip Technology Inc. Curtis Kell Kell Laboratories An auto-location system can dynamically detect the position of a specific sensor, which is useful when tires are rotated. The heart of the TPM system is the Sensor/Transmitter (S/TX) device and it is based on Microchip's rf PIC12F675. INTRODUCTION This document explains a typical tire pressure monitoring (TPM) system specifically intended for automotive use. It serves as a reference to design a real-world system based on various Microchip products. A TPM system primarily monitors the internal temperature and pressure of an automobile's tire. There is a variety of system approaches to follow, although this one is a rather prehensive auto-location system. SYSTEM PONENTS The TPM system consists of the following major ponent. - - - - - Sensor/Transmitter Device RF Receiver Module Low Frequency (LF) mander Device Control Unit Pressure Vessel (Tire) FIGURE 1: TIRE PRESSURE MONITORING (TPM) SYSTEM  2004 Microchip Technology Inc. DS00238B-page 1 .. Sensor/Transmitter (S/TX) Device There are typically five S/TX units per vehicle, one per wheel, and the spare tire. Each unit has a unique serial number enabling the system to distinguish between each tire. When mounted within a vehicle tire, the S/TX periodically measures internal tire pressure, temperature and battery condition. It then sends a RF signal posed of the measured information to a central receiver. The device described in this document is based on Microchip's rf PIC12F675 and the pressure and temperature sensing is performed by the Sensonor SP-13, a sensor IC (.sensonor.). The unit is also equipped with a LF receiver unit, used to municate to the S/TX device and to enable it from a Sleep state. RF Specific: - Transmit Frequency: 315 MHz - Transmit Interval: 60, 15 or 5 seconds (LF selectable) - Power Output: +9 d Bm into 50 Ω load - Operating Current - Transmit: 12.5 m A at max...