Electronic off-board Communication

Electronic off-board Communication

USB -UART

UART communication earlier was using RS232 level converters, with the wide use and acceptance of USB; USB to UART became popular and most of the times we will use USB to UART converter. Laptops do not have RS232 terminal, but you may get to see them on older desktop.

CP2102 / CP2104, FT232, CH340, PL2303 are the most widely USB to UART chips in the market. You can buy the modules from online or from an electronics shop in your locality.

Consideration in buying UART - 

1. If you use only RX and TX line for communication with a micro-controller you may go ahead and buy the adapters with 4 pin viz Vcc, Gnd, Tx, Rx.
2. If your interface needs 3.3V then you need to consider a USB module with 3.3V output. But this 3.3V can supply a maximum of 50mA.
3. To program an Arduino board you will require a USB UART module with RX, TX and DTR pin.
4. To program ESP modules you may need modules with TX, RX, DTR and RTS pins

In general if you may buy boards with all 9 pin out so you can use it for any application involving 5V logic.

RS485

RS485 Module

RS485 is aphysical media OR the hardware used for longer distance communication up to and little beyond 1 km. Lesser the baud rate longer the distance. MAX485 IC is available in local market. The interface will have input signals 'Rx', 'Tx' and 'DE' (Drive enable. Output signals are ''A' and 'B' which are the differential lines and get connected to other distant device.
You may use software like MODBUS or your own UART protocol to communicate to other RS485 devices.
You will find a lot of RS485 IC and Modules to interface with the micro-controllers

Ethernet

W5100 from Wiznet and ENC28J60 from Microchip are widely used Ethernet chips/Modules. Ethernet cable can be 100 meters in length and offers 10/100Mbps speed.
The easiest way to start is using an Arduino Ethernet shield, this shield is supported by numerous examples.

GSM

Arduino GSM Sheild

2G SIM800 and M95 modules are common. Some manufacturers use Ublox modules also, they are little costlier tthan SIM800 and M95 2G modules. For most of the sensor and control application this is fine.
EC20, EC25 are the 4G modules available with a higher price tag, but all application discussed here do not need the speed of 4G. Until 2G is supported SIM800, M95 2G modules can be used.
BG96 is another 4G NBIoT module from quicktel, but NBIoT is not available in India at the time I am writing this post.
Control from GSM modules can be achieved either using SMS / Dialing the phone number /Establishing a GPRS connection.

Bluetooth

Bluetooth HC05, HC06 and HM10 modules have flooded the market. Most of the modules are used for serial communication and hence you will find Rx and Tx pins to connect to any micro-controller. Bluetooth module as system on chip (SoC) are available from manufacturers like Nordic semi. Nordic  module - 518xx series Bluetooth module are also famous but costs almost 5 - 10 times more than HC05.
ESP32 is also a good choice as it has bluetooth SoC and is supported by examples in arduino IDE and ESP32 IDF programming environment. 

WiFi

Node MCU WiFi Module

Most popular for WiFi communication are the ESP8266 and ESP32 modules. Modules from Atmel, Microchip are also available but not as cheap as ESP modules.
You will find galaxy of application and learning material with support of code examples and youtube has 100's of video to make your learning very easy with ESP32 modules.

LoRa

LoRa stands for long range and was initiated by SigFox company to support low data rate and longer distance to provision IoT sensors. Over a period of time this has gained importance and Lo-Ra modules are available even in local market.
These modules mostly use 433 MHz and 868 MHz frequency band for communication and can achieve distance up to 15 Kms in open space. Tests on this have showed in city limit where geography is occupied with buildings and vehicles it can achieve a range up to 1.5 KMs

Infrared

The most common use of infrared communication is in TV remote controls. Using IR LED and a TSP13xx receive you can transmit UART signals. This is one of the cheapest communication and requires line of sight and max 10 meters to operate.