GPRS/GSM module knowledge summary (functional application selection and debugging)

At present, the second generation mobile communication technology (GSM) is gradually developing to the third generation mobile communication technology 3G), and GPRS (General Packet Radio Service) as a transition technology from GSM to 3G becomes a bridge connecting GSM and 3G.

GSM is the abbreviation of Global System for Mobile Communications, which means global mobile communication system and is one of the world's major cellular systems. GSM is based on the narrowband TDMA system. It was launched in Europe in the 1980s. The convenience of the GSM communication method is that it provides a smart card, ie SIM card, and the card can be separated, so that the user can replace the GSM communication terminal without replacing the SIM card ID. . The GSM communication mode also allows the user to send and receive short messages of no more than 160 words in length, which facilitates the practical application of the GSM communication network and the monitoring device.

GPRS is the English abbreviation of General Packet Radio Service, which is a new packet data bearer service developed on the existing GSM system. It provides medium speed data transfer by utilizing unused TDMA channels in the GSM network. It can provide a higher rate than the existing GSM network, and users can use various high-speed data services in the mobile state through GPRS, including sending and receiving mai1, and performing internet browsing.

GPRS enables users to send and receive data in end-to-end packet transmission mode. Since the wireless resource adopts dynamic allocation mode, one user can allocate multiple time slots, and one time slot can also be shared by multiple mobile stations. Although the user is always connected with the network, the channel resources are occupied only when the data is transmitted, and the original circuit. Compared with the type of service, the user's use of the GPRS service will have the characteristics of short link-building time, high data transmission rate, and low cost.

The most fundamental difference between GPRS and existing GSM voice systems is that GSM is a circuit switched system and GPRS is a packet switched system. Therefore, GPRS is more suitable for intermittent, bursty or frequent, small amount of data transmission, and also for occasional large data volume transmission. Compared with GSM circuit-switched data transmission, GPRS packet switching technology has the advantages of “always on”, “flow metering”, “reverberation fast” and “transmission high speed”. It should be noted that modules with GPRS have GSM function. . The GSM module only contains GSM functionality.

The GPRS/GSM module is also often called the mobile phone module. That is because the mobile phone is composed of CPU, GPRS/GSM module, and IO device. When we understand the GPRS module and compare it with our own mobile phone, some problems will change. It's very simple.

Similar to mobile phones, when we use the GPRS module as a communication device, we use a single-chip microcomputer, ARM, PLC, PC, etc. to send AT commands through the serial port communication to control the GPRS/GSM module to send text messages, make calls, and link to the Internet (need to know the target) Fixed public network IP + port number), (only one at a time) to send the information we need to the target phone and server. In turn, we can control devices with GPRS/GSM modules by using mobile phones and computers, just like using mobile phones in our daily life, we can send text messages, call, QQ, WeChat, and Internet. With your phone, you can know the status of your device, no matter how far you send a text message to control your device.

Everyone knows that you need to enter your mobile phone number to send text messages or make phone calls. Therefore, we need to use the AT command to input the target number when we send text messages and call the control module. If you need to make a call, you need to send ATD*****5814 through the serial port, and you can return to ok.

Let's talk about the GPRS network communication function, which is also the most exciting and most utilized function of the GPRS module, because:

First, it embeds the TCP/IP protocol. We can complete the TCP/IP communication only by sending the destination information and data information through the serial port. We can use it as a gateway to facilitate remote login and viewing.

Second, using GPRS for network communication, we only need to pay the traffic fee, a few dollars can get dozens or even hundreds of megabytes of traffic, the amount of data is much larger than the SMS package of the same price.

In general, the GPRS module has GSM functions, namely SMS and telephone services, and the hardware cost is similar. This is why many companies now choose the GPRS/GSM module instead of the GSM module alone.

We use PC to browse the web, log in to the mailbox, QQ chat, etc. need to access the corresponding server. To browse the webpage, you need to have a link or enter the server's network address. When you run a chat tool such as QQ, you need to have the code to access the server inside the program. The final resolution is the server's fixed IP address and port number. The IP address here must be a fixed public IP or a fixed public IP and port number that can be mapped through the login router. Please note that this is also a necessary network condition for debugging the GPRS network function and establishing a GPRS monitoring center server.

The IP of the GPRS module is dynamically allocated by the service provider. Generally, it cannot be used as a server. The two GPRS modules cannot directly disconnect from the central server for network communication!

Public network access mode: The IP address obtained by the computer on the Internet is a non-reserved address on the Internet. The computers on the public network and other computers on the Internet can access each other at will.

For example, GTM900 opens a TCP link: AT%IPOPEN="TCP", "219.135.251.239", 60000<Enter><Line Feed>

Return CONNECT where 60000 is the port number, which can be set by yourself. The IP address and port number are the IP and address of the destination you want to send.

After the configuration is completed, the data can be sent. The English letters and numbers are sent in ASCII code. For example, sending data 1234@, it is easy to query the ASCII comparison table in sending, 31 and 32 represent the characters '0', ' 1', and so on, AT%IPSEND="3132333440"

Return %IPSEND: 15 returns OK

The reception of data is similarly simple. Specific questions such as whether the IP address is a public network, router IP address mapping, and other functions are described in detail in our manual. It can be said that we can use a single-chip microcomputer plus a GPRS/GSM module to make a simple mobile phone. If our hardware and software are powerful enough, then an Iphone out of the cottage is not a problem! Of course, our goal is not to make an ordinary mobile phone in the cottage, but to be a super mobile phone that can realize the system we require!

About DTMF dual-tone multi-frequency I believe that everyone is no stranger to using the mobile phone to dial 10086 or 10010 two customer service center calls, we will voice prompts "Put Mandarin please press 1", "Query service please press 2" , "..", and so on, if we press the corresponding button here, it will enter the next step. . . So how does the 10086 or 10010 service center know which button we pressed? Ok, then let's reveal the answer, they are using the DTMF voice decoding function. When we make a phone call with a device with DTMF function, we can control the operation of the device by pressing the button on the mobile phone/landline, such as relay pull-in, motor work and alarm. Therefore the DTMF module is usually used in conjunction with the GPRS/GSM module.

The Internet of Things is an important part of the new generation of information technology. Covers a wide range of applications from sensors and controllers to cloud computing. Products and services in smart home, transportation and logistics, environmental protection, public safety, intelligent fire protection, industrial monitoring, personal health and other fields. It is the next "important productivity" that drives the world's rapid development! It is another trillion-level market after the communication network. The communication technology represented by GPRS is an extremely important part. With the GPRS communication technology, you have mastered a trillion market!

If the two modules know each other's SIM card number, they can send text messages to each other, but they cannot directly communicate with the network. The reason is that the IP address assigned by the service provider to the mobile phone is not fixed. The network address of each login may be different. I don't know if the other party's IP and port number can't communicate with the network, which is why the phone can't be used as a server.

The reason why we can use the mobile phone for QQ chat is because everyone is on the Tencent server when they log in to QQ, and the server is responsible for information transfer. If we don't want two GPRS modules to communicate with each other, we can learn from QQ and establish a server with fixed public IP and port for data transfer. It is also to build a star network.

It should also be noted here that in engineering, the two GPRS modules are generally not allowed to directly communicate with each other. It is common to use a free band of wireless modules to form a simple LAN in a small area, and each node can communicate. The central node acts as a concentrator plus GPRS as a gateway, and uploads the free LAN internal information to the website server.

DTU (Data Transfer unit) full name data transmission unit, in general, the module that can transmit data can be called DTU, Zigbee module such as CC2530 module, wireless serial port transparent transmission module such as APC230 can be called DTU.

Many customers ask if they can use the GPRS module just like a normal wireless transparent serial port module. Send data directly through the serial port (instead of command + data), which is to directly convert serial data into IP data or directly convert IP data into serial data in wireless form. From the above mentioned method of transmitting data by GPRS, we know that a separate GPRS module is not qualified for this work. But add a CPU responsible for data forwarding and control!

There are similar DTUs on the Internet with the following functions: 1) Internal integrated TCP/IP protocol stack 2) Provides serial data bidirectional conversion function 3) Supports automatic heartbeat and keeps permanent online (When there is no data communication for a long time, the mobile gateway will disconnect DTU and The connection of the center, the heartbeat packet is that the DTU and the data center send a small data packet before the connection is disconnected, so that the connection is not disconnected. In a place where there is a need, a similar method can be used. 4) Support parameter configuration, permanent save 5) Support other functions such as user serial port parameter setting, but the price is 100-200 yuan more expensive than the general GPRS module, not suitable for mass production equipment, because the cost is too high.

A Remote data acquisition, transmission and control 1. Power monitoring 2. Oilfield monitoring 3. Remote meter reading 4. Street light monitoring 5. Environmental monitoring 6. Weather monitoring 7. Water monitoring 8. Heating network monitoring 9. Meter monitoring 10. Room monitoring 11. Traffic indications 12. Coal monitoring 13. Earthquake monitoring 14. Vehicle induction 15. Water supply monitoring 16. Highway monitoring 17. Real-time monitoring of noise 18. Monitoring of key environmental pollution sources 19. Real-time transmission monitoring of water supply networks 20. Power distribution network automation Remote control system 21 remote area equipment anti-theft

B combines GPRS and base station positioning technology to locate and track personal use: personal vehicles track anti-theft, children or the elderly to prevent loss. The company uses: security, express delivery, public transportation, transportation and other companies to monitor the company's vehicle positioning and anti-theft, or to monitor the patrol personnel, so that they can better complete the work.

TC35/TC35I only supports GSM does not support GPRS can not access the Internet (Siemens)

Upgraded version of MC35/MC35I TC35 supports GSM support GPRS but does not embed TCP/IP protocol (Siemens)

SIM300/SIM900/GTM900 supports GSM support for GPRS and embedded TCP/IP protocol (SIMCOM)

GTM900B/ GTM900 supports GSM support GPRS and embedded TCP/IP protocol interface with TC35 MC55 dual-band support GSM support GPRS, and embedded TCP/IP protocol (Siemens)

MG323 tri-band can send MMS support GSM support GPRS, and embedded TCP / IP protocol interface with MC55 (Huawei)

There are very few differences between the TC35/TC35i, they are rarely available in the market, you can use their upgraded version MC35I

The SIM900 series is the latest GPRS module among them. It is an upgrade of SIM300. In terms of signal quality, processing power and comprehensive functions, SIM900 is better than SIM300. The GTM900 is similar to the SIM300, but the GTM900 series is Huawei's, which is cheaper than the SIM300.

The difference between SIM900A and SIM900 is frequency: 900A is two-frequency, 900 is quad-band, so 900A is a simplified version of 900, some special advanced functions such as DTMF dual-tone multi-frequency, MMS MMS protocol or base station positioning protocol (that is, no GPS via GSM) Network-assisted implementation of the general positioning function, also known as LBS) must be a special order for ordinary modules is not included.

Domestic SIM900A can be used, the price is 40 or 50 yuan cheaper than SIM900

The TC35 series, GTM900 series, and SIM300 series have all been discontinued. The cheaper ones on the market are generally second-hand modules. The time used is not much different from the new ones. The new ones are more expensive.

The common basic AT commands of these modules are the same, so the operation method and debugging software are common, and the single-chip microcomputer program that realizes the basic functions is also common. It should be noted that the AT command and the data sheet corresponding to the module are directly used in the development process, because the AT commands with some special functions are different.

Comprehensive factors: Learning and simple engineering applications recommend the use of GTM900 series MC55 series product development recommended SIM900A or MG323, Siemens is more expensive

A: It's very simple, it's much simpler than zigbee! Combine data and video tutorials and learn about this very useful technique in 20 minutes.

We usually use the serial port to debug the required AT command on the first computer. The AT command does not need to be recorded. When using it, refer to the instruction manual. Then ported to the serial port of the device CPU. When debugging, you can use serial debugging assistant, remote terminal and some special software developed by friends. You can choose one of the three. They are essentially the same as sending AT commands to the module through the serial port. The module itself also feeds back commands through the serial port. Use it to see your personal habits. It is recommended to use the serial debugging assistant.

When debugging the network function of the GPRS module, you need to install the network debugging assistant or the dedicated software for integrating the network debugging function on the computer. The function of these software is to simulate a server or terminal to let the module access. The module itself also sends AT commands through the serial port (host computer or single-chip microcomputer) to set and send information. These command information can be viewed by the serial debugging assistant. The specific information sent can be viewed by the network debugging assistant.