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How to Interface GSM Modem with MCU
A GSM Modem is a open & special 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 without LCD DISPLAY.
Easy to Use:-
1. RS-232 Interface/ TTL pin ON BOARD.
2. On Board AC/DC With 12VDC PIN OUT.
3. On Board Antenna/SMA Antenna.
4. Network Indication LED – Visual indication to GSM.
The GSM Modem with a simple to interface with microcontroller in serial interface.
It is used to send SMS, make and receive calls, and do other GSM operations by controlling it through simple AT commands from micro controllers and computers. One of the most popular SIM300 module for all its operations, RS232 interface which can be used to easily interface the modem to micro controllers and computers.
The modem consists of all the required external circuitry required to start projects with the SIM300 module like the power regulation, external antenna, SIM Holder, etc.
Features:-
- SIM300 GSM module is External use.
- Standard serial RS232 interface for easy connection to computers and other devices.
- Provides serial TTL interface for easy and direct interface to microcontrollers.
- Power, RING and Network LEDs for easy debugging.
- Onboard 3V Lithium Battery holder with internal RTC.
- Used for GSM based Voice communications, Data/Fax, SMS,GPRS and TCP/IP stack.
- Controlled through standard AT commands.
- Onboard wire antenna for better reception.
- The SIM300 allows an adjustable serial baud rate from 1200 to 115200 bps.
- Operating Voltage: 7 – 15V DC.
Modem a low power consumption of 0.25 A during normal operations and around 1 A during transmission use 1.5 A current ratingpower supply.
APPLICATIONS:-
- SMS based Remote Control & Alert.
- Security Applications.
- Sensor Monitoring.
- GPRS Mode Remote Data Logging.
How it works?
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. At this stage you can start using Modem for your application.
Programme to send receive SMS.
IMPORTANT:-
Before interfacing with MCU, it is best practice to first try all these commands with PC with the use of Terminal software. AT commands and then proceed with development.
void main()
{
initADC(); // setup ADC
serialInit(); // setup 9600 serial communication
while(1)
{
printf(“ATn”);
delayms(2000); // 3 sec delay
printf(“AT+CMGF=1n”);
delayms(2000); // 3 sec delay
printf(“AT+CMGS=”09524802005“n”);
delayms(2000); // 3 sec delay
printf (“CH#1=%bu “, getADC(1)); // sends ADC value as SMS
putchar(26); // Ctrl-Z indicates end of SMS and transmit message
delayms(2000); // 3 sec delay
}
