SIM900 avec commandes AT

SIM900 GSM GPRS Shield Top Hardware Overview
SIM900 GSM GPRS Shield Bottom Hardware Overview

LED Status Indicators

There are three LEDs on the SIM900 GSM/GPRS shield which indicates connectivity or power status. By observing these LEDs you can get a visual feedback on whats going on with the shield.

LED Indicator on SIM900 GSM Shield

PWR: This LED is connected to the shield’s power supply line. If this LED is on, the shield is receiving power.

Status: This LED indicates SIM900’s working status. If this LED is on, the chip is in working mode.

Netlight: This LED indicates the status of your cellular network. It’ll blink at various rates to show what state it’s in.

  • off: The SIM900 chip is not running
  • 64ms on, 800ms off: The SIM900 chip is running but not registered to the cellular network yet.
  • 64ms on, 3 seconds off: The SIM900 chip is registered to the cellular network & can send/receive voice and SMS.
  • 64ms on, 300ms off: The GPRS data connection you requested is active.

The operating voltage of SIM900 chip is from 3.4V to 4.4V. To keep supply voltage safe at 4.1V, the shield comes with a high current, high accuracy, low-dropout voltage regulator MIC29302WU from Micrel – capable of handling load currents up to 3A.

DC Jack, Power Selection & MIC29302 on SIM900 GSM Shield

You can add an external power supply to the shield with the 5.5mm DC jack, to which you can connect any 5V-9V DC wall adapter you have. Next to the DC jack, is a Slide Switch to select the power source labeled EXTERN. To use external power source (2A min), move the slider as shown above.

The SIM900 GSM/GPRS shield uses UART protocol to communicate with an Arduino. The chip supports baud rate from 1200bps to 115200bps with Auto-Baud detection.

With the help of jumpers you can connect (RX,TX) of the shield to either Software Serial(D8,D7) or Hardware Serial(D1,D0) of the Arduino.

UART Selection Jumper Settings on SIM900 GSM Shield

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