TC35-type short message transceiver module in the gas monitor of
CO gas concentration monitor is used to measure CO in ambient air-related content in a portable intelligent instruments. At present, the domestic CO Gas Monitor and Control Center, the most common data communication through the CAN bus, RS 1 485 1 232 bus or RS-bus to complete. RS 1 232 bus communication distance is 12 m, up to 15.4 m; RS 1 485 communication distance is 1200 m. CAN bus to the direct communication distance of up to 10 km. Either way, however, has a distance limit. But the final decision of the control center of fixity. With the GSM mobile communications networks, the rapid popularity and competition becoming increasingly fierce. GSM module as a major GSM network access equipment. Applied more and more widely, and has developed a variety of optimism applications. Such as GPS / GSM (SMS) mobile vehicle monitoring positioning system; room monitoring, remote maintenance system: mobile data query securities trading and information inquiries; data acquisition system; Mobile: POS machines and mobile payment system: Mobile IC card phone, fixed - wireless access systems; mobility data and Intemet access. However, the short message module has not yet applied in CO gas detection instruments. The author presents a short message through the GSM transceiver module for communicating with the SMS Center, CO gas monitor design.
2 TC35 module
TC35-type module is the main function of the terminal components from the GSM baseband processor, power supply application specific integrated circuit, rf circuit and flash memory and other components, responsible for GSM cellular devices in the audio, data and signals, embedded software part of the implementation of the application interface and all the GSM protocol station functions. Cellular baseband processor contains all of the wireless part of the mold, the number of conversion function, in order to meet the GSM, PCS cellular subscribers growing market demand. In the case of no external circuitry will be able to support FR, HR, and EFR voice and channel coding. RF Circuits based in part on SMARTi. Module antenna cable connected to the GSC type of 50Ω connectors. TC35 module suitable for the smallest power of GSM cellular devices. The application of this cellular equipment parts man-machine interface (MMI). Through the serial port (RS232) to access to TC35. TC35 through the 40-pin ZIF connected cellular application part, ZIF connector to provide control data, audio signals and power line application interface. End-system operating voltage of 5 VDC. Since TC35 burst peak current consumption of up to 3 A. Therefore, the device plus the regulator must be enough to provide the rated current conditions. In the terminal. Switching Power Supply using LM2596 completion of 12V to 5V conversion. As a TC35 terminal power. It should be noted is. Completed by the LM2596 switching power conversion needs of high-power inductors and capacitors. To increase the energy storage capacity. TC35 to meet the power requirements.
3 CO gas monitor system structure
GSM short message sending and receiving capabilities with a portable CO gas concentration monitor the structure shown in Figure 1. Monitoring instrument developed by the author is mainly used for public places and certain production workshop in the CO concentration in air monitoring. Battery as a power supply. CO sensor N1 choose not special chemical Co., Ltd. of Japan NAP production of a 505-type electrochemical sensors. The sensor output current and the linear relationship between the concentration of CO gas (UOUT = 70 nA ± 10 nM / l × 106). A1 (OP90) can guarantee that the working electrode and reference electrode equipotential. Sensor output OμA ~ 70μA current through the Aa (OP90) converted to 0 V ~ O. 7 V voltage, to ensure that when the CO concentration of 0 ~ 10-3 A3 output of 0 V ~ 2.5V, in order to meet the MD converter U. I (ADS7822) the input requirements. OP90 has an internal zeroing circuitry. Allow instrumentation amplifier to provide a true zero-input zero-output operations. The temperature characteristics of NAP with a 505 to 3 435 K constant B of the NTC thermistor to compensate for temperature over compensated. Its output at a 10 ℃ ~ 50 ℃ can meet within the required precision. Ul (ADS7822) of the reference voltage through the 5 Ω resistors and capacitors formed on a Vcc power supply filter received. Supply its own high-frequency noise filter. The A / D converted data give as gifts U2 (89LV/51) microcontroller, is stored in the U7 (AT24C08) in the. CO gas concentration monitor for liquid crystal display module can display the concentration values and concentration curves. And through short messaging communication module with the control center.
4 mcu control of the TC35 module
The system only uses the short messaging functionality. Therefore, use only the TC35 data input and output interfaces. Note that TC35 is a data communications equipment (DCE) to connect to, rather than as an ordinary modem, data terminal equipment (DTE) to connect. As shown in Figure l. TC35's BXDO corresponding microcontroller. RXD, TC35's TXD0 corresponding microcontroller rXD. TE35 data interface work in the CMOS level (2.65 V), microcomputer control and communications of the FC35 signal level transitions. This system through the completion of 7404-type OC gate level conversion. The system power-up, in order to make TC35 into working condition. Must give the IGT plus a time delay is greater than: 100 ms low pulse. Level decreased the duration should not exceed 100 ms. Post-IGT should be kept high (3.3 V). IGT when the driver supply voltage can not be lower than the TC35's 3.3V, otherwise the TC35 can not be activated. TC35 data input / output interface is actually a serial UART, in line with ITU-RS232 interface standard. It has fixed parameters: 8 data bits, and l-bit stop bit. No parity bit. Baud rate is 300 b / s ~ 115 kb / s option. I set to the system is 9600 b / s. ZIF connector to a 6-pin SIM card interface. CCIN which is used to detect SIM card is plugged. SYNC pin connector control lamp state. In order to determine the working status of TC35. Short Messaging SCM control subroutine. The process shown in Figure 2. One. This includes the serial port initialization speed, wireless network, and set the text mode login PDU mode.
5 SMS sent and received to achieve
TC35 uses Hayes AT commands. Microcontroller to adopt the correct AT commands on the TC35 module is initialized to receive and send short message. The control of short message are three kinds of modes: Block mode, PDU mode and Text mode. Block model requires the use of manufacturers to provide driver support. At present, PDU mode has replaced the Block mode, the Text mode does not support Chinese. Therefore, this system uses PDU mode to receive and send short message. TC35 starts automatically sent to the microcontroller ~ SYSSTART, said the module can work properly, and then the following AT commands to control the short message module: Network Registration: AT + CREG? Set PDU mode: AT + CMGF = 0 to send SMS messages (PDU) mode: AT + CMGS = 019 0DOA0891683108401505f011000d91683167866040f20008a9044f60597dla (sent to convert it to ASCLL yards). By the MCU to send AT + CMGL; O0D 0A query command can be found if there are unread text messages. Return the following format:
+ CMGL: 2,0,, 260891683108401505F0240D91683167866040F20008507032418095000665E94EOA597DOK
Receive data formats are explained as follows: + CMGL: 2,0,, 26, (2: Article II; 0: No reading); 26: The length of the short message
TC35 Module controlled by the CO gas monitor, the advantage of control center with a removable, covering a wide range of real-time, good, high reliability and security is good. To GSM network as a wireless transmission network, short message service affordable, suitable for remote and mobile monitoring central station management. Have a very broad application prospects.
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