If you are looking for a compact GSM/GPRS module, you can get the SIM800L from most eBay traders. It is not the most judicious choice, but you can build your own basic GSM projects with a cheap modem for a couple of dollars. SIM800L is a minuscule GSM module that offers 2G GSM/GPRS data, and supports SIMCOM enhanced AT commands. Because it uses the serial communication method, it’s easy to interface with the UART of almost all popular microcontrollers. There are 12 connections in total (6×2 rows) on the SIM800L module and, surprisingly, one row contains all of the connections required to interface with a microcontroller like the venerable Arduino!
To begin, you need only a power supply and a serial port. Because the breakout board comes without an integrated voltage regulator, be prepared to set up an external 3.4- to 4.4-V power supply for that purpose. Based on my experience, the module is a bit power-hungry and the current consumption can be up to 2 A in peaks. If the power supply can’t cater the requisite current well, the module will shut down/reset in the middle of the action. As for the serial port connection, just pick up a suitable USB-to-serial converter. While most of the eBay sellers claim their SIM800L modules to be 5-V-logic-tolerant, the official datasheet defines the maximum high level to be 2.8 V. This calls for a “tricky” logic-level converter to work with 5-V logic circuits (luckily, no add-ons needed for a 3.3-V logic interface). You can follow the tried and tested schematic shown below to use the SIM800L module in real-world projects. The hardware includes an onboard fixed voltage regulator and a simple logic-level handler to make the setup suitable for most DIY projects.
After the completion of the hardware setup, insert a trusted SIM card into the SIM slot of SIM800L module, attach a USB-to-serial device on the UART header (see next figure), and power up the hardware. Next, open your favorite serial communication program and configure it to use the correct serial device at 115200 baud with 8N1 (8 data bits, no parity check, 1 stop bit). If nothing shows up, do an initial test by typing “AT” and wait for the “OK” response.
The onboard LED indicator will blink once every two to three seconds when it has completely registered the SIM to a network. When the LED indicator is blinking every second, this means that the SIM800L is still searching for a network to register onto. If the LED indicator does not blink, recheck the power supply to enusre that it provides plentiful current and precise output voltage. Note that the SIM800L module requires voltage in range of 3.4 to 4.4 V. If proper voltage is not provided, the module will give under- and overvoltage warnings.
Now you can play with basic commands to gain insight into the basic functionality and way of operation of the SIM800L module. And, together with the AT command reference, other promising features can be easily discovered and explored. For a complete list of AT commands, download the SIM800 Series AT Command Manual from https://www.waveshare.com/w/upload/2/20/SIM800_Series_AT_Command_Manual_V1.09.pdf .
From my workbench.
For now, this is a preface guide (yes, there’s room for more and more). I already have a microcontroller-based SIM800L project in queue that will eventually show up here. Later I will also discuss more enhanced practices in the next installment of this article, scheduled to be published within two weeks.
And here is the link of a well-tried and tested DIY GSM project: http://www.electroschematics.com/10760/arduino-gsm-home-security-alarm-system/ :: An old one, it seems, but it suits the needs!