Today, GSM networks are widely-used, whether for making calls or sending SMSes. But some places need urgent messages like in colleges, railway stations, events, share market and so on, and this information should be in real-time. This project is an experiment to give a start to the era of sending messages in real-time. It is about writing the message, which is to be displayed on mobiles, and sending it as an SMS to the receivers. The received message is fetched into a microcontroller (MCU) and, after authentication, is displayed on an LCD screen.
Circuit and working
Circuit shown in Fig. 1 operates using a 12V power supply (connected across CON1). An Arduino MCU requires only 5V but a GSM modem requires 12V. As Arduino Uno has an inbuilt 5V voltage regulator, a common 12V supply can be used for the whole system.
The brain of the circuit is Arduino Uno MCU board (BOARD1). A 16×2 LCD display (LCD1) is used for receiving and displaying the messages. Pins of LCD1, namely, RS, EN, D4, D5, D6 and D7 are connected to Arduino digital pins 12, 11, 5, 4, 3 and 2. When you want to show some information or message, you send an SMS to the GSM modem. Then, Arduino’s MCU reads the GSM modem and sends it to the LCD. Here, the LCD is used in 4-bit mode, which means only four data lines are required to display the data.
GSM modem SIM900A (connected with CON2 and CON3) sends the commands in text mode to Arduino Uno using an RS232 interface. CON3 is connected with DB9 connector of the GSM modem. RS232 voltage levels are at ±12V, whereas both MCU input and output operate at 0V to +5V. Since RS232 is not compatible with the MCU, MAX232 (IC1) is utilised to enable the communication between the GSM modem and Arduino Uno by converting RS232-level signals to TTL-level signals. Rx (DB9.3) and Tx (DB9.2) pins of the GSM modem are connected through IC1 at Tx and Rx pins of Arduino, respectively.
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