TC35 wireless gas test system hardware circuit

　　The design of CO gas monitor based on TC35 GSM module has the main feature of being able to use SMS for data transmission. The wireless communication module TC35 is introduced in detail, and the application of TCC35 short message transceiver module in CO gas monitor is given. CO gas concentration monitor is a portable intelligent instrument used to measure the CO content in the relevant ambient air. At present, the data communication between domestic CO gas monitor and control center is most commonly completed through CAN bus, RS485 (＄49.9800) bus or RS232 (＄780.5000) bus. The communication distance of RS232 (＄780.5000) bus is 12 m, and the maximum can reach 15.4 m; the communication distance of RS485 (＄49.9800) bus is 1200 m. The direct communication distance of CAN bus can reach up to 10 km. But no matter which method has distance limitation. And it ultimately determines the fixity of the control center. With the rapid popularization of GSM mobile communication network and the increasingly fierce competition. As a major GSM network access device, GSM module is increasingly used and has developed a variety of promising applications.

　　The TC35 module is the main functional component of the terminal. It consists of a GSM baseband processor, a power supply dedicated integrated circuit, a radio frequency circuit, and a flash memory. It is responsible for processing audio, data, and signals in GSM cellular devices. The embedded software part executes the application interface and all GSM protocol station functions. The baseband processor contains all analog-to-digital conversion functions of the cellular wireless part to meet the growing requirements of the GSM and PCS cellular user markets. It can support FR, HR, and EFR voice and channel coding without external circuits. The radio frequency part is based on the SMARTi (＄580.2800) type circuit. The antenna cable in the module is connected to a GSC type 50Ω connector. The TC35 module is suitable for GSM cellular devices with the lowest power. The application part of this cellular device constitutes the man-machine interface (MMI). TC35 can be accessed through the serial port (RS232 (＄780.5000)). TC35 connects to the cellular application part through a 40-pin ZIF, and the ZIF connector provides an application interface for control data, audio signals, and power lines. The operating voltage of the terminal system is 5 VDC. Since the peak current of the sudden power consumption of TC35 can reach 3 A, the external voltage regulator must be able to provide the rated current. In this terminal, the LM2596 (＄0.9108) switching power supply is used to complete the conversion from 12V to 5V as the power supply of the TC35 terminal. It must be noted that the switching power conversion completed by the LM2596 (＄0.9108) requires high-power inductors and capacitors to improve the energy storage capacity and meet the power consumption requirements of TC35.

　　Structure of CO gas monitor system

　　The structure of the portable CO gas concentration monitor with GSM short message sending and receiving function is shown in the figure. The monitor developed by the author is mainly used for monitoring the CO concentration in the air of public places and some production workshops. The battery is used as the power supply. The CO sensor N1 uses the NAP-505 electrochemical sensor produced by Japan Nemoto Special Chemical Co., Ltd. The sensor output current is linear with the CO gas concentration. A1 (OP90) can ensure that the working electrode and the reference electrode are at the same potential. The sensor output current of 0μA~70μA is converted into 0 V~O by Aa (OP90). 7 V voltage is used to ensure that the output of A3 is 0 V to 2.5 V when the CO concentration is 0 "10-3, so as to meet the input requirements of the MD converter U.I (ADS7822 (＄1.9551)). OP90 has an internal zero adjustment circuit, allowing the instrument amplifier to provide true zero input and zero output operation. The temperature characteristics of NAP-505 are compensated with an NTC thermistor with a constant B of 3435 K. After temperature compensation, its output can meet the accuracy requirements within the range of -10℃"50℃.