What is GSM?GSM stands forGlobalSystem forMobile communications. GSM is a second generation wireless communication standard developed for voice communication with a bearer service called short message service or SMS. In 1982 it was recognized as a standard for digital wireless communications and was first adopted in Europe and then by Asia, Africa etc.GSM has the advantage of using SIM (SubscriberIdentityModule) cards.Subscriber Identity ModuleThe subscriber identity module (or SIM card) is a key feature of a GSM cell phone. The SIM contains the subscription profile and address book. Although the SIM card contains account information that prevents or enables certain services, the handset (cell phone) is the device that locks the user into a specific phoneWhy do we need GSM?GSM is used for the purpose of intimating about accident to concerned authorities. A GSM modem is a specialized type of modem which accepts a SIM card, and operates over a subscription to a mobile operator, just like a mobile phone. From the mobile operator perspective, a GSM modem looks just like a mobile phone. The board which we are using is SIM908 module. SIM908 module is a complete Quad-Band GSM/GPRS module which combines GPS technology for satellite navigation. Quad-Band GSM covers frequency ranges 850MHz, 900 MHz,1800MHz, 1900MHZ.Following are the characteristics of the module: Point-to-point MO and MT SMS cell broadcast Text and PDU mode Features of GSM: Mobile Frequency Range Rx: 925-960 Tx: 880-915 Multiple Access Method : TDMA/FDMA Duplex Method : FDD Number of Channels :24 (8 users per channel) Channel Spacing :200 kHz Modulation :GMSK (0.3 Gaussian Filter) Channel Bit Rate :270.833Kb When triggered by the controller the SIM module sends a prewritten message with dynamic location details to the numbers as programmed by the coder.The LED of the shield shows the status of the GPRS+GPS module. The table below shows the meaning of the blink of the LED.Getting Started Insert SIM card: Press to remove the tray from the SIM cardholder. After properly fixing the SIM card in the tray, lock the tray in the slot provided. Connect Antenna: Screw the RF antenna on the RF cable output provided. ConnectRS232Cable to the Host device: (Cable provided forRS232communication) Connect the power Supply (12V-AC/DC) to the power jack. Network LED indicating various status of GSM module eg. Power on, network registration & GPRS connectivity. After the Modem registers the network, led will blink in step of 3 seconds.

Trouble Shooting

Note: whenGSM modempowers on the auto baud is enabled, user must first to send the A to synchronize baud rate. It is recommended to wait 2 to 3 seconds before sending AT character. After receiving the OK response, PC and modem are correctly synchronized. Ensure the the sim card holder/ connector has the SIM card. It is risky to connect power supply not preferred by the reference user manual

BASIC AT COMMANDS1.To check the modem:AT{Press Enter}OK2.To change sms sending mode:AT+CMGF=1{Press Enter}OK3.To Read SMS in Text mode:AT+CMGR= no.Number (no.) is the message index number stored in the sim card. For new SMS, URC will be received on the screen as +CMTI: SM no. Use this number in the AT+CMGR number to read the message.Example:AT+CMGR=1{Press Enter}+CMGR: "REC READ","+917708283043","","10/05/21, 20:52:20+22"

4.To Send SMS in text mode :AT+CMGS=mobile number press enterOnce The AT commands is given > prompt will be displayed on the screen.Type the message to send via SMS. After this, press ctrl+Z to send the SMS.If the SMS sending is successful, ok will be displayed along with the message number.Example:AT+CMGS=9884467058{Press Enter} < Hello GSM Modem CTRL+Z5.To make a voice call:ATD9884467058;{Press Enter}6.To Redial last no:ATDL{Press Enter}7.To Hang up or Disconnect a call:ATH{Press Enter}8.For receive incoming call:ATA{Press Enter}9.To set a particular baud rate:AT+IPR=?{Press Enter} {To view the baud rate values}AT+IPR=0 {To set the modem to auto bauding mode}10.Operator selection:AT+COPS?{Press Enter}OKAT+COPS?+COPS: 0, 0,"AirTel"OKRelated Article