How to interface GSM and GPS devices to controllers?

Indian 10:38 AM

All the IoT connectivity around us is mainly dependent on how the sensors are around us connected to internet. For Internet connectivity, there are two sources, either wired or wireless. Wireless connection is the way to go when it comes to sensors located in remote places where there is no chance of wired connection. Two major connectivity are used as a part of wireless - Wi-Fi and Cellular. The GSM/GPRS modules or the 3G/4G/5G modules are we are talking here are basically the devices which help in cellular connectivity.

1. Sensors interface to the Microcontroller or Processor

2. Microcontroller or Processor connects to the cellular module

3. Cellular module shall have an internal or an external antenna acting as a transducer converting electrical to RF and helps to transmit the data

While 2G/3G/4G/5G modules help in cellular connectivity, the GPS (Global Positioning System) modules help to track the location information. This could be GPS (US), Galileo (EU), GLONASS (Russia), BeiDou (China), NavIC (India). The ultimate aim of all these is to provide the location information where the GPS module is located. The location information shall be received from satellite launched by countries we mentioned above.

These modules 2G/3G/4G/5G or GPS are used in commercial systems like Mobiles, tracking systems and provide connectivity and tracking.

Now let us look at how these modules shall be interfaced to Microcontroller or processor.

GPS-to-Microcontroller:

For GPS systems, there is only reception required. The GPS module receives data in different formats like GPRMC, GPGGA, GPGSV, etc and passes to Microcontroller/processor which further process the data and use it based on need.

GSM-to-Microcontroller:

GSM module acts based on the AT commands. Microcontroller/Processor passes AT commands to GSM modules which responds based on the commands. HTTPS requests are sent to server from GSM module where the communication is established there by data is exchanged. This is just like our mobiles which work based on SIM and cellular connectivity. There is cellular connectivity required for the data to be exchanged.

GSM modules come with integrated controller which can be used for writing the application program. Based on memory space demands and other interfacing requirements, decision shall be taken by the designer whether to use external microcontroller or internally controller. While all these are all modules, there are modems, Gateways available in the market which is a full-fledged solution to be used in applications.

The current generation of 4G/5G modules interface to the processor over SDIO. There are PCIe based boards which are available from Sierra Wireless. Please, check this module from Sierra Wireless for more details:

https://www.sierrawireless.com/products-and-solutions/embedded-solutions/products/em9190/

While all this looks straight forward, there are modules which require level translation. Some modules have 1.8V digital logic, where as controllers/processors generally have a logic levels of 3.3V over the I/O interface. In these cases, a level translator is required between Controller and Modules.

The level translator could be a simple BJT based circuit as shown below or an IC which is available from various manufacturers like Texas Instruments, NXP.