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Definition:
GSM, which stands for Global System for Mobile communications, reigns (important) as the world’s most widely used cell phone technology. Cell phones use a cell phone service carrier’s GSM network by searching for cell phone towers in the nearby area. Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication.
GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership.
INTRODUCTION
SIM 300 is a GSM modem with a simple serial interface. SIM 300 modem can accept any GSM network operator SIM card and act just like a mobile phone with its own unique phone number. With this module one can send/receive sms, connect to internet via GPRS and receive calls. The modem can either be connected to PC serial port directly or to any microcontroller. When purchasing purchase the entire board. As it comes with RS232 to TTL converter and ethernet port Also do check the module by calling a few times when in the shop.
SIM300 GSM modem works for supply voltages from 3.4V to 4.5V. This voltage is difficult to generate as we dont get a standard regulator at this voltage. Do not give 5V directly to the modem as it is above its absolute maximum ratings .
Here is a simple circuit which we can build using standard 5V regulators which are easily available. I use these circuits regularly in my projects as they are easy and require less external components to function and no design work. The 5V regulators are given a input of 5V which reduce the voltage to around 3.6 to 4V (due their own internal dropout voltages) which is the required voltage for the SIM300 modem . The 1000uF electrolytic capacitor is very necessary as it gives stability to the GSM MODEM power supply when it consumes large currents during Calling or sending SMS. If the capacitor is not added and your 5V power supply is not capable of delivering required currents during Call and sending SMS then the modem will keep getting reset . I recommend using a 5V 2A power adaptor for the 5V input.
The regulator used is a NCP1117ST50T3 SMD 5V 800mA SOT223 regulator which is easily available. You can also use a standard 7805 regulator also if you don't get the NCP1117. But the dropout voltage of the 7805 is large which is around 3V. Due to this sometimes the 7805 circuit may give lesser voltage than 3.5V if there are any other heavy loads connected to the 5V power supply. But normally it should work.
There are two LEDs on the board. One is power LED and the other is the network LED. When you insert your SIM card into the slot and power ON the device the power LED will be turned ON. After few seconds the network LED will start blinking after an interval of 3 seconds. If this happens it means signal is proper but if it is blinking faster it means that there is no network. If your mobile phone has network then this module should have network at the same location(provided the antenna is connected.) Make a call and it should ring. Do it a couple of times before purchasing from a store.
MODEM SPECIFICATIONS:
The SIM300 is a complete Tri-band GSM solution in a compact plug-in module.
Featuring an industry-standard interface, the SIM300 delivers GSM/GPRS900/1800/1900Mhz performance for voice, SMS, data and Fax in a small form factor and with low power consumption.
The leading features of SIM300 make it deal fir virtually unlimited application, such as WLL applications (Fixed Cellular Terminal), M2M application, handheld devices and much more.
1. Tri-band GSM/GPRS module with a size of 40x33x2.85
2. Customized MMI and keypad/LCD support
3. An embedded powerful TCP/IP protocol stack
4. Based upon mature and field proven platform, backed up by our support service, from definition to design and production.
General Features:
• Tri-band GSM/GPRS900/1800/1900Mhz
• GPRS multi-slot class 10
• GPRS mobile station class –B
• Complaint to GSM phase 2/2+
i. -class 4(2W @900MHz)
ii. -class 1(1W @/18001900MHz)
• Dimensions: 40x33x2.85 mm
• Weight: 8gm
• 7. Control via AT commands
• (GSM 07.07, 07.05 and SIMCOM enhanced AT commands)
• SIM application tool kit
• supply voltage range 3.5…….4.5 v
• Low power consumption
• Normal operation temperature: -20 ’C to +55 ‘C
• Restricted operation temperature : -20 ’C to -25 ‘C and +55 ’C to +70 ‘C
• storage temperature: -40 ‘C to +80 ‘C
Specifications for Fax:
Group 3 and class 1
Specifications for Data:
• GPRS class 10: max 85.6 kbps (downlink)
• PBCCH support
• coding schemes Cs 1,2,3,4
• CSD upto 14.4 kbps
• USSD
• Non transperant mode
• PPP-stack
Specifications for SMS via GSM/GPRS:
• Point to point MO and MT
• SMS cell broadcast
• Text and PDU mode
Compatibility:
At cellular command interface
Specifications for voice:
1. Tricodec
-Half rate (HR)
-Full rate (FR)
-Enhanced full rate (EFR)
2. Hands free operation
(Echo cancellation)
Drivers:
Microsoft windows mobile RIL driver
MUX driver
Interfaces:
• Interface to external SIM 3v 1.8v
• 60 pins board-to-board connector
• Two analog audio interfaces
• Keypad interfaces
• LCD interface
• RTC backup
• AT commands via serial interface
• Dual-Serial interfaces
• Antenna connector and antenna pad
Approvals:
• FTA
• Local type approval
• CE
Power supply:
The power supply of SIM300 is from a single voltage source of VBAT= 3.4V...4.5V. In some case, the ripple in a transmit burst may cause voltage drops when current consumption rises to typical peaks of 2A, So the power supply must be able to provide sufficient current up to 2A.
For the VBAT input, a local bypass capacitor is recommended. A capacitor (about 100μF, low ESR) is recommended. Multi-layer ceramic chip (MLCC) capacitors can provide the best combination of low ESR and small size but may not be cost effective. A lower cost choice may be a 100 μF tantalum capacitor (low ESR) with a small (1 μF to 10μF) ceramic in parallel, which is illustrated as following figure. And the capacitors should put as closer as possible to the SIM300 VBAT pins. The following figure is the recommended circuit
Power supply pins on the board-to-board connector:
Eight VBAT pins of the board-to-board connector are dedicated to connect the supply voltage; four GND pins are recommended for grounding. BACKUP can be used to back up the RTC.
Minimizing power losses:
Please pay special attention to the supply power when you are designing your applications. Please make sure that the input voltage will never drops below 3.4V even in a transmit burst during which the current consumption may rise up to 2A. If the power voltage drops below 3.4V, the module may be switched off. Using the board-to-board connector will be the best way to reduce the voltage drops. You should also take the resistance of the power supply lines on the host board or of battery pack into account.
Monitoring power supply:
To monitor the supply voltage, you can use the “AT+CBC” command which include three parameters: voltage percent and voltage value (in mV). It returns the battery voltage 1-100 percent of capacity and actual value measured at VBAT and GND.
The voltage is continuously measured at intervals depending on the operating mode. The displayed voltage (in mV) is averaged over the last measuring period before the AT+CBC command was executed.
Power up and power down scenarios:
Turn on SIM300
SIM300 can be turned on by various ways, which are described in following chapters:
• Via PWRKEY pin: starts normal operating mode (see chapter 3.4.1.1);
• Via RTC interrupt: starts ALARM modes (see chapter 3.2.1.2)
Note: Only enter AT command through serial port after SIM300 is power on and Unsolicited Result Code “RDY” is received from serial port.
Turn on SIM300 using the PWRKEY pin (Power on):
You can turn on the SIM300 by driving the PWRKEY to a low level voltage for period time. The power on scenarios illustrate as following figure
When power on procedure complete, SIM300 will send out following result code to indicate the module is ready to operate:
Turn on SIM300 using the RTC (Alarm mode):
Alarm mode is a power-on approach by using the RTC. The alert function of RTC makes the SIM300 wake up while the module is power off. In alarm mode, SIM300 will not register to GSM network and the software protocol stack is close. Thus the parts of AT commands related with SIM card and Protocol stack will not accessible, and the others can be used as well as in normal mode.
Use the AT+CALARM command to set the alarm time. The RTC remains the alarm time if SIM300 was power down by “AT+CPOWD=1” or by PWRKEY pin. Once the alarm time expires and executed, SIM300 goes into the Alarm mode. In this case, SIM300 will send out an Unsolicited Result Code (URC):
ALARM MODE:
During Alarm mode, using AT+CFUN command to query the status of software protocol stack; it will return 0 which indicates that the protocol stack is closed. Then after 90S, SIM300 will power down automatically. However, during Alarm mode, if the software protocol is started by AT+CFUN=1, 1 command, the process of automatic power down will not available. In ALARM mode, driving the PWRKEY to a low level voltage for a period will cause SIM300 to power down (Please refer to the power down scenarios