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TC35i GSM module based on the temperature detection system

In Electronic Infomation Category: T | on April 26,2011

Traditional method of temperature measurement, the user directly reads the temperature detection device or through a wired network to the temperature data to the testing room. However, if the detection point distance of a bad environment, but can not guarantee real-time scene was the case, using conventional detection methods is clearly not. Therefore, the monitoring of the wireless transmission of temperature data points and TL431ID datasheet and detection of remote wireless control is necessary. To address the traditional system can not keep abreast of detecting environmental information issues, the use of GSM module TC35i based on the original add wireless control functions, breaking the traditional wired distance constraints, and TL431ID price and the GSM network coverage, through the GSM public network SMS platform, in a timely manner The temperature measurement and TL431ID suppliers and control points to send the information to the user. Users can also send text messages to control the heating or cooling equipment.

1 Technical Overview and Features

GSM GSM is developed by the European standards for digital mobile phone network, and its purpose is to develop a common global standard to use a mobile phone network. Siemens TC35i, after following the development of the industrial TC35 GSM module, shown in Figure 1. It is a short message support Chinese industrial GSM module can work in GSM900 and GSM1800 dual band, TC35i of 1 to 5 pin is the positive power supply input pin, the recommended value is usually 4.2 V, 6 to 10 pin is the power to . 11,12 for the charge pin, you can add lithium batteries, the external output voltage of 13 and 14 for the ACCU-TEMP to the negative temperature coefficient thermistor, for lithium battery charging protection control. 15 feet is to start foot IGT, after the system power state to enter the work TC35i, must give IGT plus a 100 ms before boot.

Figure 1 TC35i module physical map

2 Hardware Design

2.1 function module There are 1602

system liquid crystal display module, TC35IGSM module, STC89C52 microcontroller, temperature sensor 18B20, relay parts, and power system block diagram shown in Figure 2. STC8 9C52 as the system processor, containing 8 kB of Flash memory. 18B20 collected as part of the system temperature, the temperature data sent nine digital single chip, single chip data processing after the temperature through the liquid crystal display. Serial port interrupt occurs when the MCU, the MCU starts TC35i module reads the content of messages and phone numbers, if the message content and the content of pre-set match to perform the appropriate actions, such as sending "openl" to open the relay 1, the implementation of a successful SCM After the message through the GSM network feedback to the user. If the content does not match the information will be deleted.

Figure 2 System Block Diagram

2.2 Temperature acquisition module

Temperature acquisition partly DS18B20, it is a single-bus digital temperature sensor, temperature measurement range is -55 ~ 125 , -10 ~ +85 degrees in between the accuracy of 0.5 , the temperature values ??for the amount of 9 read out, the temperature digital conversion time 200 ms, DS18B20 is the "first-line bus," the transmission, improved anti-jamming capability, suitable for harsh environments. Because of its higher cost DS18B 20 Therefore, the temperature of the system selected it as part of the collection. SCM in connection with the 18B20 to use pull-up resistor, size of 4.7 k, 18B20 and MCU connection only takes one I / O interfaces, shown in Figure 3.

Figure 3 DS18B 20 and MCU connection

2.3 TC35i Module

TC35i module consists of a ZIF connector, Flash, antenna interface, the transmitter module and the baseband processing module 5 parts, block diagram shown in Figure 4. TC35i baseband processor as the core, which dealt mainly with the terminal within the GSM voice and data signals, and cellular radio equipment covering all the analog and digital functions. TC35i 40 pins through a ZIF (Zero Insertion For-ce, zero resistance socket) connector leads.

Figure 4 block diagram

TC35i can support standard AT commands, TC35i involved in the design of 18 feet (RXD0), 19 feet (TXD0) and 15 feet (IGT) Other pin function is not used, 18,19 with pins as serial port communication 15 connections P1, 0, 15 pin microcontroller to a low level can be automatically activated TC35i module, TC35i and STC89C52 serial port can be connected directly, the other microcontroller level according to the need for conversion, TC35i and STC89C52 specific connection shown in Figure 5. During communication, the sender will set a good message content from the senders phone to send out, through the short message center forward, TC35i received short message stored in the SIM card, the controller module to read the short message 89C51 extract useful information as needed, and finally the information will remove the SIM card, so to complete a one-way data transmission. TC35i Single Chip Design to receive messages using interrupted scan, once the information reaches TC35i module, the controller calls the receiver program to receive text messages.

Figure 5 TC35i and SCM connection method

2.4 Temperature Control parts

Automatic temperature control system, users need to set the temperature according to when the acquisition when the temperature is below the set temperature, the system open relay 1, when heating equipment work. When the temperature is higher than the set temperature acquisition system open relay 2, then cooling equipment work. Users can also send text messages via cell phone to remotely turn on or off any road relay. The system uses a power relay, which can be used for 220 V mains electrical equipment. For added security, the use of optocoupler isolation played a role of high and low voltage, connect the circuit shown in Figure 6.

Figure 6 relays and MCU connection Circuit

3 system software design

3.1 instruction part of the

Microcontroller through the serial port to send AT commands and TC35i communication, commonly used AT commands shown in Table 1. AT the beginning of each AT command to order to enter the end of the control of SMS There are 3 main ways: Block Mode, Text Mode based AT command AT command-based PDU Mode, the system uses the PDU Mode to send and receive messages.

Table 1 Common AT commands

Example, to send a "successful operation" to 13488097615 (3184087916F5), the first must convert the UNICODE character code, the conversion "operation successful" UNICODE code 64CD 4F5C6210 529F, AT commands are (1) AT + CMGF = 0: Set TC35i the PDU format. AT + CMGS = 023??: Instructions for sending short messages, of which 023 representatives of the number of bytes of data content, but not including a 00, the text for each increase of 1 plus 2 bytes will. Byte sent is set to 23, says 0011000D91 (81) 3184087916F50008010864CD4F5C6210529F, meaning the code as shown in Table 2.

Table 2 Development of the information code format

3.2 part of the program

3.2.1 main program

Main program flow chart shown in Figure 7, after the initial boot TC35i module detects SIM card is installed, the initialization can be successfully received PDU format message, when message arrives module, TC35i can phone number for sending messages to read, and content analysis, if the content is in line to perform the operation, and to this number back a corresponding message content, or delete the message.

main program flow chart of Figure 7

3.2.2 content processing

Void read_sms () is the process of handling some of the content of information, if any messages received, sent cell phone number first reading and then compare the content, processed message back to the original phone number, if it is an error message will be removed.

4 Conclusion Communication from the TC35i module

temperature monitoring system, the advantage of covering a wide range of real-time, high reliability, cheap. The GSM network as the wireless transmission network for frequent application to send a small amount of data, but also applicable in remote areas, set up lines of communication difficulties. And in unattended areas or unattended systems, applications to send short message service data fit, the operator need only a cell phone through the test points can understand the temperature, and can remotely open the heating and cooling equipment, the development prospects better.

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