Circuit design using TC35I wireless data transmission and GSM communication module

　　Wireless data communication circuit design

　　Wireless data communication circuits are mainly responsible for the short-range wireless data exchange between motor vehicles and fixed base station systems. It consists of core chip nRF401 and its accessory components. nRF401 is a dual-channel, high-performance, low-power dedicated wireless communication chip with an operating frequency of 433.93/434.33MHz. The operating voltage is 3.3v and the maximum communication rate is 20kbps. It can be directly connected to the serial port of the microcontroller for asynchronous communication to achieve Data sent and received. No need to encode the data. The data input terminal DIN is connected to the TxD terminal of the microcontroller, and the data output DOUT terminal is connected to the RXD terminal of the microcontroller. In this circuit, the communication rate is designed to be 19.2 kbps. The circuit principle is shown in Figure 3.

　　Transfer files for PCB proofing

　　Wireless data communication unit circuit

　　GSM communication module circuit design

　　The GSM communication module adopts SIEMENS' TC35I. TC35I is a special module specially designed by SIEMENS for GSM communication. It has voice, data, fax and point-to-point SMS functions. It works in the EGSM 900 and GSM 1800 frequency bands. It weighs only 10g and can operate normally within the range of 3.5~4.8V. The main instructions defined by AT Commands Interface Version 8.5 can be executed well, and there are more than 20 extended instructions.

　　The TC35I interface consists of 40-core cable. Among them, pins 1~5 are connected to the "+" terminal of the battery, pins 6~10 are connected to the "-" terminal of the battery, and pins 11~12 are the DC power input terminals, which can input 8~20V/500mA DC power. There is an automatic charging control circuit inside. The 15-pin IGT is for module startup control, and the 31-pin EMERGOFF is for shutdown control. They are both active at low level, and can also be turned on and off through commands. Pin 17 is the ringing output, pin 18 Rx is the serial data output, pin 19 TX is the serial data input, pin 32 is the working status indicator output, and pins 24~29 are connected to the SIM card. The interface circuit with the microprocessor is shown in Figure 4. The communication rate is 19.2kbps.

　　Interface circuit between TC35I and microprocessor

　　All instructions for TC35I can be downloaded from the SIEMENS website. The vehicle-mounted user mobile payment system is composed of a low-cost AT89C4051 microcontroller with a working power supply of 3.3V. The base station is composed of a high-speed and high-performance 77E58-40 microcontroller to complete wireless data communication and identity authentication functions. CCD vehicle model identification is completed by another independent processing unit.