Sim900 gsm module

 GSM/GPRS sim900 module(gsm module arduino)

Human-machine or machine-machine communication can be considered as a new type of dialogue possible. Thinking of GSM telecommunication technology, it immediately comes to mind voice communication, sending and receiving SMS and MMS and mobile internet. We can therefore imagine, using these services provided through GSM technology, that remote control and control of machines, alarm systems and surveillance are possible.

The user: allows you to send a message to a GSM module by a mobile phone (The message contains coded information for the commands).
GSM module: allows you to receive or send text messages and communicate with an electronic card through a serial communication (UART). The commands used in this connection are AT COMMANDS.
Electronic card: allows you to communicate with the GSM module, read messages, send commands and execute the various processes such as processing, decoding and storing information, displaying messages, etc.

Short Message Service (SMS)

The Short Message Service (SMS) consists of sending and receiving alphanumeric messages with only a mobile terminal (mobile GSM). Short SMS messages are specified by ETSI. There are two ways to send an SMS message, either in PDU (Protocol Description Unit) mode or in TEXT mode. The TEXT mode, not supported by most mobile phones and GSM modules, allows to send SMS without coding prior to scanning.
On the other hand, in PDU mode, which is the basic mode, the message to be sent is codified into a sequence of hexadecimal characters before it is transformed into a binary train in order to increase the number of characters that an SMS can contain. Different types of encoding are used to switch from PDU to TEXT mode. The most answered is the one called «7-bit GSM alphabet» which offers the maximum number of characters to send (160 characters). For this type of encoding each character is code on seven bits.

Description of the GSM/GPRS sim900 module

Among the various models offered by SIMCOM, we chose the GSM module based on the 900 SIM circuit.With an industrially compatible interface, the SIM900 provides the representation of GSM/GPRS 850/900/1800/1900MHz. It is able to work in voice, data, FAX and above all, the most interesting for us, in SMS mode. Designed with a very powerful single-piece processor integrating the AMR926EJS kernel, it allows us to take advantage of small dimensions and cost-effective solutions.

The module has a bracket for the necessary SIM card and an MMCX connector for connecting a small RF antenna also supplied by SIMCOM. All inputs and outputs needed to drive the module are available on a 68-point connector. With a tiny 24mm x 24mm x 3 mm configuration, SIM900 can comply with almost any space conditions in our M2M (machine to machine) applications, especially for slim and compact design requirements.

General features

Voice, Data and SMS Transmission
Power supply 3.4 V to 4.5 V, typically 3.8 V
Frequency bands GSM 850 MHz, EGSM 900 MHz, DCS 1800 MHz, PCS 1900 MHz
Absorbed Current: GSM900: 147 mA (900 mA max)
                               GSM1800: 127 mA (700 mA max)
                               GSM1900: 113 mA (650 mA max)
Transmit power Class 4 (2 W) for GSM/EGSM Class 1 (1 W) for DCS/PCS bands
SIM card reader Integrated in the module, supports 3v and 1.8v SIM cards 
Operating temperature - 40°C to + 85°C 
External Coil by MMCX Connector 
Mass 3.4 g 
Size GSM07.07 and GSM07.05 
GPRS Data Services GPRS multi-slot class (MSC) 10 (4+1, 3+2), GPRS PBCCH/PCCCH support, GPRS Class B and CC 
SMS messages (Short Message Service) It is thus possible to send small amounts of data via the mobile network (ASCII or hexadecimal data) 
Embeds a TCP/UDP stack To send data on a web server 
Control with AT commands Standard commands: GSM 07.07 and 07.05 Extended commands: SIMCOM AT Commands

The SIM 900 module

The SIM 900 module is written on the following figure:

A SIMCom Logo
B Module name
C Module part number
D Module serial number and barcode
E IMEI Module and Bar Code
F Identification authenticated by FCC
G Logo authenticated by CE

Data Characteristics

• Class 10de GPRS: maximum 85.6 Kbps (downlink).

• Data transmission CSD , GPRS.

• SIM900 integrates TCP/IP protocol and extended TCP/IP AT commands that are very useful for data transfer applications.

• Non-transparent mode.

Features for SMS via GSM/GPRS

• Sending out the text cells.

• The supported modes are text mode and PDU mode.

AT COMMANDS

The communication tool used to control modems and phones with another machine is ATCOMMANDS. These are instructions used in a system such as sending a text or making a call for example.
AT: Attention code. It is the prefix of a command line that tells the modem that a command or sequence of commands will be sent.

The command does not exceed 556 characters

ME (Mobile Equipment): mobile phone

TE (Terminal Equipment): maybe a computer or a microcontroller

TA (Terminal Adapter): provides the link between the ME and the TE

TA and ME form a single entity. A standard mobile phone for example or a GSM terminal contains both the TA and the ME in its box.

The TE is a separate entity. For example, it could be a computer with a serial port or an electronic circuit based on a microcontroller that implements a serial port.

Types of AT COMMANDS and responses

Test command : The ME returns the list of parameters and value ranges defined with the corresponding write command by internal processes

Command to read : This command returns the currently defined parameter value

Command to write: This command defines the user-defined parameter values.

Execution command: The execution command reads the non-variable parameters affected by internal processes in the GSM.

SMS service dedicated AT order 

AT+CSMS Courier Service Selection
AT+CPMS Memory area selection for storage
of SMS
AT+CMGF SMS format selection (PDU or TEXT)
AT+CSCA Setting the Email Centre Address
AT+CSDH Displays the SMS settings in TEXT mode
AT+CSAS Configuration backup
AT+CRES Restore default setting
AT+CNMI Indication concerning a new SMS
AT+CMGL List SMS stored in memory
AT+CMGR Reading an SMS
AT+CMGS Sends SMS
AT+CMSS Sending an SMS stored in memory
AT+CMGW Writing an SMS.
AT+CMGD Clears an SMS