Short distance wireless communication in the design of RFID system for automobile applications
source: 21IC time: 2012-05-15
1.2 RF circuit
The radio frequency part use TI CC1020 as the radio frequency control unit, the chip is a single chip narrowband real industry's first UHF transceiver, FSK / GFSK / OOK 3 modulation methods, the minimum channel spacing of 50 kHz, which can meet the multi-channel narrow application (402 ~ 470 MHz and 804 ~ 94O MHz band) of the strict requirements, multiple frequency band can be switched freely, the working voltage of 2.3 ~ 3.6 V, very suitable for integrated extended to mobile device to use as wireless digital or electronic label. The chip to comply with the EN300 220.ARIB STD-T67 and FCC CFR47 Part15 specification.
Selection of carrier frequency of 430 MHz working frequency band, the band for the ISM band, accord with national standard wireless management committee, without applying frequency point. Using the FSK modulation method, has higher anti-interference ability and low error rate, using forward error correction coding technology, improve the ability of data against burst and random disturbances, in the channel bit error rate of 10-2, the actual error rate can be obtained from 10-5 to 10-6. In the open line-of-sight conditions, baud rate is 2A Kbs, big chuck antenna (length 2m, a gain of 7.8 dB height 2m) when the data transmission distance can reach up to 800 m. The RF standard provides 8 channels can meet the combination of multiple communication. Because of the narrow band communication technology, enhance the communication stability and anti-interference. RF section diagram as shown in figure 3.
Power supply system of 1.3
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Power system consists of photovoltaic cells as part of daily work of power supply and lithium batteries as backup battery combined power supply. In the light of better conditions by solar energy for energy storage battery charging, every day to ensure a certain illumination time can basically meet the requirement of OBU daily working needs, service life greatly extended the battery backup, and prolong the working life of the OBU. For often in outdoor running vehicle use, can be collected to sunlight for solar cells.
1.4 system development environment
The system development environment are as follows: 1) IAR Embedded Workbench for MSP430 compiler; 2) design tool PADS PCB Design Solutions 2007 Beith circuit board.
2 system program design of
The program uses a modular design, using C language. Mainly consists of 4 parts: in the main program module, communication module, peripheral circuit, interrupt processing module and storage module. The main procedure initializes, various parameters control unit configuration and the peripheral module configuration and initialization; communication program module of RF chip configuration and a 433 MHz transceiver; peripheral circuit module of system external LED indicator, voltage detection, voice prompts to keys and other treatment interruption and storage; module interrupt processing system and the record store. The main program flow shown in figure 4.