{"id":61615,"date":"2022-06-06T15:30:47","date_gmt":"2022-06-06T19:30:47","guid":{"rendered":"https:\/\/www.engineersgarage.com\/?p=61615"},"modified":"2022-06-22T01:17:08","modified_gmt":"2022-06-22T05:17:08","slug":"articles-raspberry-pi-sim900a-gsm-gprs-modem-interfacing","status":"publish","type":"post","link":"https:\/\/www.engineersgarage.com\/articles-raspberry-pi-sim900a-gsm-gprs-modem-interfacing\/","title":{"rendered":"RPi Python Programming 20: Interfacing the SIM900A GSM-GPRS modem and hacking earphones"},"content":{"rendered":"

In the previous tutorial<\/strong><\/a>, we learned how to use Raspberry Pi\u2019s (RPi) serial hardware port for serial data communication over the universal asynchronous receiver\/transmitter (UART) protocol. Most of the embedded devices have the\u00a0<\/span>UART port for exchanging console data<\/a><\/strong>. In fact, most of the sensor modules that are designed for peer communication with controllers\/computers have the UART port for data communication. So, there are several sensor modules that can be interfaced with Raspberry Pi using its UART port.\u00a0<\/span><\/p>\n

Remember that RPi\u2019s UART port is 3.3V and it should be connected with the compatible serial port. If the other device has a different UART voltage level, the suitable voltage level shift or serial adaptor must be used. For example, a device with the 5V TTL UART port can connect to RPi\u2019s serial port of using a 5 to 3.3V TTL Logic Shifter.<\/span><\/p>\n

Similarly, RPi’s UART port can be connected to the USB interface of a device using a USB-serial board. It can also be connected to the RS-232 port of a device using the RS-232-serial converter.\u00a0<\/span><\/p>\n

The serial ports of sensors and modules can be directly or indirectly interfaced with those of Raspberry Pi and to any desktop computer using a USB-serial board.\u00a0<\/span><\/p>\n

As\u00a0<\/span>Python<\/a><\/strong>\u00a0<\/strong>is platform-independent, the script that works on RPi to receive serial data from a sensor can be used on any desktop computer by simply changing the serial port name.\u00a0<\/span><\/p>\n

In this tutorial, we\u2019ll learn how to interface a SIM900A GSM-GPRS modem with\u00a0<\/span>Raspberry Pi<\/a><\/strong>\u00a0<\/strong>and with any desktop computer. We\u2019ll also discuss how to hack an ordinary earphone to make and receive voice calls over a SIM900A modem.\u00a0<\/span><\/p>\n

Wireless modems<\/span><\/strong>
\n<\/span>Wireless connectivity is a widely accepted solution for data communication over long distances. For M2M IoT solutions, mobile connectivity is the only resort to guarantee data transfer with mobile devices and remotely-deployed \u201cThings.\u201d There are many wireless modules available from different vendors that can be used for data communication over a mobile network. These wireless modules are generally classified by the mobile network technology (2G, 3G, 4G, or 5G) or by the technology platform they use (GSM\/GPRS, GSM\/GPRS+GNSS, WCDMA\/HSPA\/HSPA+, LTE, NB-IoT, or GNSS).<\/span><\/p>\n

These wireless modules are capable of communicating data in the form of voice calls, SMS, GPRS, faxes, and the Internet (TCP\/IP, IP, HTTP, and FTP protocols).\u00a0<\/span><\/p>\n

SIMCOM is one of the largest vendors of wireless modules. Different wireless modems available from SIMCOM Limited for mobile connectivity are listed in this table:<\/span><\/p>\n

\"\"<\/a><\/p>\n

On the basis of the technology platform, the SIMCOM modules are listed in this table:<\/p>\n

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Although 4G and 5G wireless modules are advanced modems offering the high speeds and features of 4G and 5G technologies, 2G wireless modules are still widely used in embedded applications. The 2G wireless modules are less costly and offer an optimum wireless solution where speed and latency are not an issue.<\/p>\n

The SIM900A GSM-GPRS modem<\/strong>\u00a0\u00a0<\/strong>
\n<\/span>SIM900 is a 2G wireless module that offers a Quad-Band 850\/900\/1800\/1900 MHz GSM-GPRS solution. The modem features GPRS multi-slot class 10\/class 8 (optional) and supports CS-1, CS-2, CS-3, and CS-4 GPRS encoding schemes.\u00a0<\/span><\/p>\n

This ultra-compact modem requires a supply voltage of 3.2 to 4.8V. It can be controlled via AT commands (GSM 07.07, 07.05, and SIMCOM enhanced AT Commands), which can be communicated through the serial interface (UART), I2C, and SPI.\u00a0<\/span><\/p>\n

It also has a single interface to an external SIM 3V\/1.8V in which the\u00a0<\/span>Mini-SIM (2FF Form Factor), Micro-SIM (3FF Form Factor) and, NanoSIM (4FF Form Factor)<\/a><\/strong>\u00a0<\/strong>can be plugged in.\u00a0<\/span><\/p>\n

The modem is equipped with a GPIO, PWM, ADC, and an analog audio interface so that it can have a MIC and audio and speaker input, as well as a display and keypad interface. It also comes with a built-in RTC.\u00a0<\/span><\/p>\n

Some of the prominent features of SIM900A modem are listed here:<\/span><\/p>\n

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The SIM900A modem has this pin diagram:<\/p>\n

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The SIM900A modem has this pin configuration:<\/p>\n

\"\"<\/a>\"\"<\/a><\/strong><\/span>Hardware & wiring<\/strong>\u00a0\u00a0<\/strong>
\n<\/span>It\u2019s fairly easy to wire the modem.\u00a0<\/span><\/p>\n