The Low Power Research Of Remote Tire Pressure And Temperature Monitor

At present, the electronic technology is applied very popularly and the electronic products have lots of characteristics such as small bulk, light weight and easy to take. So it is very necessary to improve the reliability and reduce the power consumption of the products. The design of the low power products has become the certain developing direction in the product design. At the same time, because of the improvement of the manufacture technics level and in particular the maturity of the CMOS techincs, the low power products can be produced in the society. There are several methods about the design of the low power products: using the CMOS circuit as soon as possible; turning off the free circuit when the system is working; selecting the low voltage and the working frequency of the whole circuit.The low power of the remote tire pressure and temperature in TPMS is designed in this paper. This system can not only reach the real-time monitoring capability, but also reduce the energy consumption. The final purpose of this paper is to make the RTPM module work a long time under one lithium battery which supplies the power for the whole RTPM module. During the design of this system, it includes two aspects: the low power design of the hardware and the software.(1) The low power design of the hardware of the systemThe purpose of the low power design of the hardware is to give a hardware support to optimize the energy consumption of the whole system. The low power design of the hardware at circuit level focuses on low power characters of the processor and peripherals, designs the power supply circuit of the processor and peripherals: First, the paper analyzes and designs the low power characters of the integrate circuit . At present, the making technics of the electronic products has converted from technics TTL to technics CMOS. The biggest character of the technics is the micro-power which is the circuit foundation of low power design of the integrate circuit. After doing the analysis about the energy consumption principle of the technics CMOS, we get some methods to reduce the energy consumption of the integrate circuit: minishing the value of the load capacitance,reducing the value of the working voltage and reducing the activity of the switches; Second, the microprocessor,sensor and the RF transmitter that we chose do have the great characters about the energy consumption. The microprocessor PIC16F877 which is supplied by the Microchip Corporation is a kind of CMOS chip with 8 bits. It not only has the low power sleeping module that can save the energy, but also it is made with the high-speed CMOS FLASH/EEPROM technics and designed by complete static state. Under 5V/4MHz, the working current is below 2mA. Under 3V/32KHz, the working current is about 20μA and under the common waiting state and the working current is only 1μA. The sensor that we choose is chip SP12 which is produced by the Infineon Corporation. In the low power aspect, it has the original advantage of adopting the working module of awaking the instantaneous state. When it works at the sleeping module, the power is only about 0.6mA·s. The RF transmitter nRF401 doesn't need to encode with Manchester code so that it saves the energy of encoding consumption. The waiting current is only 8μA and the transmitting power is about 10dBm. Because of the characters of low working voltage, it usually uses in the period of low power design.(2) The low power design of the software of the systemThe low power design of the software has a great effect in reducing the whole system's energy. At first, we use the best power managing arithmetic to manage the whole system's energy. It's named as Dynamic Power management (DPM). Because of using this arithmetic, if some parts don't work, they will be cut down. And if there are some tasks for them to do, the power will be supplied for them. That is to say that even if under the condition of having the least parts running or making the load smallest, the system can provide the nice service and capability response. Second, during the working of the RTPM module, the energy consumption that the RF transmitter takes up is very lager in the whole system when it transmits the digital signal. So it needs to reduce the transmitting time of the RF signal when it is not necessary. This method can reduce the energy consumption. The technical scheme that we design is described below: In the driving process of the automobile, the pressure and temperature sensor of RTPM collects data about the pressure and temperature and transmits them to theMicroprocessor. The Microprocessor analyzes the data in detail. There are two circumstances: First, if the value of the pressure and temperature data that are collected has no change or changes a little .That is to say that the value is in the scope that we define at the beginning. If the automobile drives at the low speed, the RF transmitter will be in the sleeping module. If the speed of the automobile is very high, the RF transmitter will be in the state of sending the data which will be sent less in one minute. The second circumstance is that if the value of the pressure and temperature data is not in the scope that we define at the beginning or changes very quickly. When the automobile drives at the low speed, the RF transmitter will be in the state of sending the data which will be sent less in one minute. If the speed of the automobile is very high, The RF transmitter will send the data very quickly -that's to say the data will be sent more in one minute. We use this method to reduce the transmitting time of the RF transmitter.After testing, it's proved the system basically reaches the real-time capability of monitoring the pressure and temperature. And after estimating the life of the lithium battery, this scheme reaches the purpose of reducing the system's energy consumption.