• Arduino Uno or Mega (x2) for 10 USD.
• Dragino shields (x2) for 20 USD.
• 868 MHz Antenna (x2) for 5 USD.

• RadioHead: The Packet Radio library for embedded microprocessors can be downloaded from http://www.airspayce.com/mikem/arduino/RadioHead/ or from this direct link.
• Arduino IDE: Specific OS versions can be downloaded from https://www.arduino.cc/en/Main/Software.

This tutorial is written for :

• Arduino IDE 1.6.9.
• RadioHead 1.61.
• Dragino hardware release v1.3.
• Mac OS 10.11.5.

Beware of the necessary modifications, if any of the previous specifications is not supported in your case.

Start by plugging the Dragino shields on the Arduino devices and mounting the antennas as shown in Fig. 1.

Figure 1. Arduino with LoRa Dragino shield.

Connect the two Arduino devices to USB ports on your computer. If this is the first time you use Arduino IDE, make sure to install the necessary USB drivers by selecting Tools > Boards Manager and installing Arduino AVR boards.

Now, you have to select the corresponding Board and Port in the Tools menu to program your Arduino. For example, you can use the following:

• For Arduino Uno: Board = Arduino/Genuino Uno Mega, Port = /dev/cu.wchusbserial1420.
• For Arduino Mega: Board = Arduino/Genuino Mega 2560, Port = /dev/cu.usbmodem141511.

Unzip the RadioHead library and copy it to your sketchbook library folder as detailed in https://www.arduino.cc/en/Guide/Libraries.

Start by setting the central frequency of the LoRa modules. For this, open the RH_RF95.cpp file and change the frequency to 868.1 Mhz:

RH_RF95.cpp

setFrequency(868.1);

Download the basic sketches that implement a reliable LoRa communication between the two modules. Open the sketches with Arduino IDE, compile and upload on the two arduino modules, respectively. On the serial interfaces, you should obtain similar results as in Fig. 2.

Bw125Cr48Sf4096 Bw = 125 kHz, Cr = 4/8, Sf = 4096chips/symbol, CRC on. Slow+long range

RH_RF95.cpp

//setModemConfig(Bw125Cr45Sf128); // Radio default
setModemConfig(Bw125Cr48Sf4096); // slow and reliable?

RHReliableDatagram.h

#define RH_LONG_TIMEOUT 8000

RHReliableDatagram.cpp

RHReliableDatagram::RHReliableDatagram(RHGenericDriver& driver, uint8_t thisAddress) 
    : RHDatagram(driver, thisAddress)
{
    _retransmissions = 0;
    _lastSequenceNumber = 0;
    //_timeout = RH_DEFAULT_TIMEOUT;
    _timeout = RH_LONG_TIMEOUT;
    _retries = RH_DEFAULT_RETRIES;
}