Power management is considered to be an important aspect in designing battery operated Tire Pressure Monitoring Systems (TPMS) as it helps to prolong the lifespan of the battery. There are several methods that can be used to design a low power tire-pressure and service monitoring system. One of the most common methods for power reduction is the duty cycle method. This thesis suggests an idea of implementing the TPMS in combination with a separate Radio Frequency Identification (RFID) circuit, especially a very low power (active or passive) RFID whose sole purpose is to detect the interrogating signal. This RFID circuit which can operate at a typical frequency of 125 kHz is used to turn ON a higher power transmitter which is initially in SLEEP state and soon after entering the active state performs the communication, updating, etc. Once the desired task is completed, the high power transmitter returns to SLEEP state or is turned off until the next interrogation.
The implementation of SLEEP mode to minimize power consumption is discussed in detail and the currents consumed by the microcontroller in SLEEP and ACTIVE modes are measured and recorded. The microcontroller in SLEEP mode consumed a current of 17μA which reduced the overall average current consumed by the microcontroller and the pressure sensor. Furthermore, this method promises an improvement in the battery life and the calculations showing this improvement are discussed with the example of an AA battery with 2800mAh battery life.