Hello friends! Today, we will send an SMS with an Arduino UNO and a SIM900D GSM module using AT commands. We will start with the connections, check that the modem can communicate with the mobile network, and then let the Arduino submit one message. You will also learn how to tell the difference between a successful command and a message that has actually reached its recipient. Libraries SIM900 Simulation Libraries Latest library: SIM900A Library for Proteus V1.1 (October 2026) Other GSM modules: SIM800L · SIM800C · SIM808 Helping Tools Serial Monitor Advance : a serial terminal window for the UART of your board Serial Monitor Expert : the serial monitor with extra debugging tools LCD Library for Proteus V3.0 : 16x2, 20x4 and I2C LCDs to show your readings The SIM900D handles the radio conn ...