Introduce the design of CO gas monitor based on NL-2007 GSM module, its main feature is the ability to apply SMS for data transmission. The wireless communication module NL-2007 is introduced in detail, and the application of NL-2007 SMS remote control alarm module in CO gas monitor is given. 1 Introduction The CO gas concentration monitor is a portable intelligent instrument used to measure the CO content in the relevant ambient air. At present, the most common data communication between the domestic CO gas monitor and the control center is through the CAN bus, RS-485 bus or RS-232 bus. The communication distance of RS-232 bus is 12 m, and the maximum is 15.4 m; the communication distance of RS-485 bus is 1200 m. The direct communication distance of the CAN bus can be up to 10 km. But no matter which way there is a distance limit. And ultimately determines the fixedness of the control center. The author proposes a design scheme for a CO gas monitor that communicates with a short message center through a GSM short message transceiver module. 2 NL-2007 module The NL-2007 module is the main functional component of the terminal. It is composed of a GSM baseband processor, power supply integrated circuit, radio frequency circuit, and flash memory. It is responsible for processing audio, data, and signals in the GSM cellular device. Execute the functions of the application interface and all GSM protocol stations. The baseband processor contains all the analog and 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 the need for external circuits. The radio frequency part is based on the SMARTI type circuit. The antenna cable in the module is connected to a GSC type 50Ω connector. The NL-2007 module is suitable for the smallest power GSM cellular equipment. The application part of this cellular equipment constitutes a human-machine interface (MMI). NL-2007 can be accessed through the serial port (RS232). NL-2007 is connected to the cellular application part through a 40-pin ZIF. The ZIF connector provides application interfaces for control data, audio signals, and power cords. The operating voltage of the end system is 5 VDC. Because the peak current consumption of NL-2007 can reach 3 A. Therefore, the external voltage stabilizing device must meet the conditions sufficient to provide the rated current. In the terminal. Use LM2596 switching power supply to complete the conversion of 12V to 5V. As the power supply of NL-2007 terminal. It must be noted. The conversion of switching power supply by LM2596 requires high-power inductors and capacitors to improve the energy storage capacity. Meet the power consumption requirements of NL-2007. 3 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 Figure 1. The monitor developed by the author is mainly used for monitoring the CO concentration in the air of public places and certain production workshops. The battery is used as the power supply. The CO sensor N1 uses NAP-505 electrochemical sensor produced by Japan Basic Special Chemicals Co. The output current of the sensor has a linear relationship with the CO gas concentration (UOUT = 70 nA ± 10 nM / l & TImes; 106). A1 (OP90) can guarantee the equipotential of working electrode and reference electrode. The sensor output OμA ～ 70μA current is converted into a voltage of 0 V ～ O.7 V through Aa (OP90) to ensure that the output of A3 is 0 V ～ 2.5V when the CO concentration is 0 ~ 10-3 to meet the MD converter UI (ADS7822) input requirements. OP90 has an internal zero adjustment circuit. Allows the instrumentation amplifier to provide true zero input and zero output operation. The temperature characteristic of NAP-505 is compensated by NTC thermistor with constant B of 3 435 K. After the temperature is compensated, its output can meet the accuracy requirement within a range of 10 ℃ ~ 50 ℃. The reference voltage of Ul (ADS7822) is connected to Vcc through a power filter composed of 5 Ω resistors and capacitors. It filters out the high-frequency noise of the power supply itself. The data after A / D conversion is sent to U2 (89LV / 51) single-chip microcomputer and stored in U7 (AT24C08). The liquid crystal display module of the CO gas concentration monitor can display the concentration value and the concentration change curve. And communicate with the control center through the short message transceiver module.
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