SIM300 is an GSM modem which can be controlled through AT Commands. In this tutorial i am going to explain how to send/receive sms, how to make/receive a call, how to send a tweet to twitter using the SIM300 modem.
I am going to use the sim300 modem with TTL output so it can be directly connected to the microcontroller ports.
Sim300 needs a power supply of 3.4v to 4.5v, but the microcontroller circuit has only 5v supply. I am just using a Diode 1N4007 in series with the Vcc of the modem. So a 0.6v is dropped across the diode and so that the modem will receive only 4.4v.
SIM300 modem used by me.
Circuit Diagram
Just connect the VCC of the modem to +5V through diode and Gnd to microcontroller ground. Then TXD pin to Pin3.0 of the microcontroller and RXD pin to P3.1 of the Microcontroller.
Dont forget you need a minimum 2A power supply, since the GSM modem consume more power at the time of sending and receiving SMS.
Circuit diagram for Interfacing SIM300 GSM modem to AT89S52
Circuit diagram for Interfacing SIM300 GSM modem to AT89S52