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Abstract: TC35T is a GSM wireless modem from SIEMENS. The main characteristics of the LV35T in remote unmanned control are introduced in combination with the P87LPC767 microcontroller, and the design of the repeater monitoring system is completed.
Keywords: short message; serial port; repeater; TC35T
Classification: TN91 Document code: B Article ID: 1006-6977 (2003) 01-0020-02
1 Introduction
In recent years, with the rapid development of the mobile communication industry, as a mobile network extension and perfect equipment - the repeater has been rapidly applied, the location of the repeater is often in remote rural areas and mountains, so maintenance is very inconvenient, In order to understand the working status of the repeater in time, the author developed a repeater monitoring system. The main functions of the system include wireless monitoring of the power supply and RF output power of the repeater to achieve unattended fault alarm and control functions of the repeater system. The basic principle of the repeater monitoring system is to utilize the wide coverage of the GSM wireless cellular network, and to transmit the working status of the repeater and related information in the form of SMS to the GSM network by means of the SMS (Short Message) service function of the GSM network. The designated monitoring center or maintenance person's mobile phone, so that the system failure is processed in time; usually, the monitoring center or mobile phone can also query the working status of the repeating station at the designated location to ensure the normal operation of the communication network. At the same time, because the monitoring system is equipped with a backup battery, it can still work for several hours when the AC power fails, so that the fault information can be reliably transmitted back to the network maintainer. This system can also be used for power and power monitoring of other automation systems.
2 TC35T features and functions
The TC35T is a GSM-specific modem from SIEMENS that delivers voice, data, short messages and faxes over the GSM network. The TC35T has a standard industrial interface and a complete SIM card reader, so the use is very simple.
2.1 Main features of TC35T
The main features of the TC35T are as follows:
â— Can work in dual-band EGSM900/GSMl800;
â—With voice, data, short message and fax transmission functions;
â— has an analog voice interface;
â— Can read and write SIM card;
â—With an RS232 interface;
â— The working voltage range is as wide as 8-30V, and the voltage range is 5.6~30V when only data is transmitted;
â— Support GSM Phase2/2+;
â— Support AT commands.
2.2 Main interface functions of the TC35T
The TC35T is packaged in a semi-finished product with an analog voice interface, RS-232, SIM card, power supply and antenna.
(1) Power interface
The power interface of the TC35T is shown in Figure 1. The functions of each terminal are as follows:
1 foot: positive power input terminal;
2 feet: empty feet;
3 feet: reset input;
4 feet: excitation input;
5 feet: empty feet;
6 angle: grounded.
(2) RS232 interface
The RS232 interface using the 9-pin D-Sub connector is shown in Figure 2. This interface is mainly used to connect the TC35T to a PC or a single-chip microcomputer. It can be controlled by software to control the TC35T as needed. The function of each pin is as follows:
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1 pin: data carrier detection;
2 feet: data reception;
3 feet: data transmission;
4 feet: data terminal ready;
5 feet: ground;
6 feet: data setting is ready;
7 feet: send a request;
8 feet: send clear;
9 feet: ringing indication.
3 system structure
Figure 3 shows the block diagram of a general monitoring system. It can be seen from Fig. 3 that the repeater with the monitoring unit distributed throughout the whole can be connected to the monitoring network by the monitoring center computer through the GSM network. The monitoring center computer runs a special visual interface monitoring software, and is equipped with a wireless modem. The fault information of the remote repeater can be transmitted back to the monitoring center at any time. The monitoring center can also query the distributed repeater at any time. Working status.
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3.1 The composition of the monitoring unit
The internal structure of the monitoring unit is shown in Figure 4. It consists mainly of a power supply unit (with battery charging and backup battery switching), a microprocessor unit (MCU) and a GSM-compliant wireless modem. The status of the repeater can be monitored by the micro-station. If a fault occurs (such as power failure, power abnormality, etc.), the system can handle the fault and convert the fault information and related data into a short message format via the wireless modem. The TC35T is sent to the BTS and then transmitted to the network operation and maintenance personnel via the GSM network.
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The monitoring unit uses P87LPC767 as the control center, and includes four parts: data acquisition, information reception, information transmission and power supply.
The MCU P87LPC767 is an 80C51 modified MCU that adds an 8-bit A/D and D/A converter consisting of the WDT watchdog, I°C bus and two analog comparators that the user wants. In addition, its power-on reset detection and undervoltage reset detection function can ensure that the drive current of the I/O port reaches 20mA, the operating speed of the P87LPC767 is twice that of the standard 80C51, and the temperature range also reaches the industrial standard -40-+ 85 ° C. The reliability of the MCU itself is excellent, and the P87LPC76x also has many features of the MCS-51 series.
The data acquisition in the system includes 220V AC sampling, 12V DC voltage sampling, 24V DC voltage sampling and RF power sampling. Wireless data transmission and reception is done by Siemens' TC35T.
The system is powered by AC and DC. AC power supply is completed by AC/DC power supply module. DC power supply is provided by 6V lead-acid battery to ensure that the system can reliably send fault information back to the monitoring center during AC power outage. In order to ensure the normal operation of the 220V AC voltage sensor, the system also designed a boost circuit, which can raise the 6V DC voltage to 12V.
3.2 Software design of monitoring unit
The software of the monitoring unit is designed in assembly language. The functions to be completed include A/D sampling control, alarm information transmission, response to control commands, control of TC35T, and automatic reset of the program. The main block diagram is shown in Figure 5.
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4 Conclusion
Short message delivery has the advantages of wide coverage, automatic transmission, low cost, good stability, etc. It can be used for remote monitoring of the environment, field data collection, reservoir water level monitoring, etc. However, since the delivery of short messages needs to be completed by the mobile switch and the short message center, its timeliness is related to the capacity of the short message center and the busyness of the mobile switch. In the case of short message congestion or traffic intensive periods, its timeliness is poor. In addition, since the maximum length of each short message specified in the GSM protocol is 160 bytes, the amount of information used each time it is transmitted cannot be too large.
references
[1]. P87LPC767 datasheet http://
[2]. RS232 datasheet http://
[3]. RS-232 datasheet http://
[4]. 80C51 datasheet http://
[5]. MCS-51 datasheet http://
[7].Siemens.AT Command Set Siemens Cellular Engines.Copyright (c) Siemens AG 2001
[8].TC35T Hardware InterfaceDescription, ,com
[9]. Zhou Ligong. Principle of P87LPC7670TP microcontroller.
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