SIM900 demonstration projects. Introduction

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1 demonstration projects Introduction is a complete Quad-band GSM/GPRS module designed by SIMCom. Featuring an industry-standard interface, the delivers GSM/GPRS 850/900/1800/1900MHz performance for voice, SMS, Data and Fax in a small form factor and with low power consumption. is designed as a DCE (Data Communication Equipment). It provides a full modem serial port, which is used for data transmission and for sending AT commands. The is integrated with the TCP/IP protocol; extended TCP/IP AT commands are developed for customers to use the TCP/IP protocol easily, which is very useful for those data transfer applications. The following demonstration projects are developed based on module: 1) Sending and receiving SMS, 2) Voice calls, 3) TCP/IP communication over GPRS. evaluation board is used to make development process easier and faster. It interfaces the directly with appropriate power supply, SIM card holder, RS232 serial port for connection with PC, handset port, earphone port, antenna and all GPIO of the. The evaluation board is shown below: Fig. 1 Evaluation Board module is controlled by a microcontroller that contains user application. Sample projects are described more detailed below.

2 Sending and receiving SMS This example demonstrates I/O control by SMS messages. Proposed device has 1 digital input (switch) and 1 digital output (LED) that are monitored and controlled by user via SMS messages. Block diagram of the device is shown on figure 2. Mobile OUT Fig. 2 Block diagram of the device for SMS communication Main tasks of this device are as follows: 1) Continuous monitoring of the digital input. When transition of the input state occurs (OFF to ON or ON to OFF), the corresponding SMS message is sent to the selected mobile phone. For example, when input state changes from OFF to ON condition, the following SMS message is sent to the selected mobile phone: Input is ON. If input condition changes from ON to OFF, the Input is OFF SMS message is sent to the selected mobile phone. 2) Control of the digital output (LED out). User controls LED state by sending corresponding SMS. When the device receives Turn ON LED SMS message, LED is turned ON by microcontroller. The following response is returned to the mobile phone: LED is turned ON. If the device receives Turn OFF LED SMS message, LED is turned OFF by microcontroller. The following response is returned to the mobile phone: LED is turned OFF. Other SMS messages that are received by this device are ignored. No response is sent back in this case. program interfaces module via. Dedicated AT commands are used for processing of the SMS messages.

3 Voice calls This application allows to make and receive voice calls. Block diagram of the device is depicted on figure 3. Mobile Speaker Microphone Answer Hang Up Fig. 3 Block diagram of the device for voice calls Microcontroller has only 2 inputs for buttons: 1) Answer or Make a call, 2) Hang Up or Cancel the incoming call. These buttons are used to answer incoming calls and hang up. Main tasks of the microcontroller are as follows: 1) Detection of buttons activities, 2) Sending appropriate AT commands to start and stop voice calls. Other work is performed automatically by module. This includes audio signal processing and transfer. The device can receive voice calls from any phone number. Voice calls can be made to only one fixed mobile. This is done for simplification purposes because no keypad is used.

4 TCP/IP communication over GPRS The proposed project demonstrates TCP/IP communication over GPRS. It allows to connect a based device that is configured as client with a PC application program that acts as server. Block diagram of the TCP client and TCP server is shown on figure 4. PC software TCP/IP Server OUT TCP/IP Client Fig. 4 Block diagram of the TCP client and server connection Main tasks of the microcontroller are as follows: 1) Configuration of the module for TCP/IP Client mode, 2) control via AT commands for data transfer, 3) Updating of the LED state, when the corresponding command received from server. Extended TCP/IP AT commands are developed for customers to use the TCP/IP protocol easily. controls module by corresponding AT commands. Data transfer is performed by module automatically. When PC application is started, dedicated port number of server is opened. After this moment server starts to listen for data from client. Meanwhile, client ( with module) tries to connect to the specified TCP/IP server periodically. If the server is closed, connection with server is not established. In this case the client tries to connect to the server again. This process continues periodically until the server will not start listening to the client. After the server starts to listen, the client establishes the connection with selected server. When the client detects connection with the server, the following message is sent to the server: Client is ready. After server receives this message, it knows that client is ready for data reception. There are several commands / messages that are responded by client in this example project: 1) Hi client. When client receives this message from server, it sends back the following message to the server: HELLO SERVER. What do you want?

5 2) Please, toggle LED. When client application receives this message, microcontroller toggles LED state. If LED state becomes ON, the following message is returned to the server: LED is turned ON. If LED state changes to OFF, the following message is returned to the server: LED is turned OFF. For demonstration purposes the following software was used for TCP server ( Fig. 5 PC software for TCP server