LoRa with Raspberry Pi — Peer to Peer Communication with Arduino

LoRa is getting increasingly popular with the advent of IoT, Connected Cars, M2M, Industry 4.0 etc. Because of its ability to communicate to long distances with very less power it is preferably used by designers to send/receive data from a battery powered Thing. We have already discussed the basics of LoRa and how to use LoRa with Arduino. Although the technology is originally intended for a LoRa Node to communicate with a LoRa gateway, there are many scenarios in which a LoRa Node has to communicate with another LoRa Node to exchange information over long distance.

In this tutorial we will learn how to use a LoRa module SX1278 with Raspberry to communicate with another SX1278 connected to a microcontroller like Arduino. This method can come in handy at many places since the Arduino could act as a Server to fetch data from sensors and send it to Pi over a long distance through LoRa and then the Pi acting as a Client can receive these information and upload it to the could since it has access to internet. Sounds interesting right? So, let’s get started.

Materials Required

• SX1278 433MHz LoRa Module — 2 Nos
• 433MHz LoRa antenna — 2Nos
• Arduino UNO- or other version
• Raspberry Pi 3

It is assumed that your Raspberry Pi is already flashed with an operating system and is able to connect to the internet. If not, follow the Getting started with Raspberry Pi tutorial before proceeding. Here we are using Rasbian Jessie installed Raspberry Pi 3.

Warning: Always use your SX1278 LoRa module with 433 MHz antennas; else the module might get damaged.

Connecting Raspberry Pi with LoRa

Before we get into the software packages, let’s get the hardware ready. The SX1278 is a 16-pin Lora module that communicates using SPI on 3.3V Logic. The Raspberry pi also operates in 3.3V logic level and also has in-built SPI port and 3.3V regulator. So we can directly connect the LoRa module with the Raspberry Pi. The connection table is shown below

You can also use the circuit diagram below for reference. Note that the circuit diagram was created using the RFM9x module which is very similar to the SX1278 module, hence appearance might differ in the below image.

The connections are pretty straight forward, only problem you might face is that the SX1278 is not breadboard compatible hence you have to use connecting wires directly to make the connections or use two small breadboards as shown below. Also few people suggest to power the LoRa module with separate 3.3V power rail as the Pi might not be able to source enough current. However Lora being a low power module should work on the 3.3V rail of Pi, I tested the same and found it to be working without any problem. But, still take it with a pinch of salt. My connection set-up of LoRa with Raspberry pi looks something like this below

Connecting Arduino with LoRa

The connection for the Arduino module remains the same as that we used in our previous tutorial. The only difference will be instead of using the library from Sandeep Mistry we will use the Rspreal library based on Radio head which we will discuss later in this project. The circuit is give below

Again you can use the 3.3V pin on Arduino Uno or use a separate 3.3V regulator. In this project I have used the on-board voltage regulator. The pin connection table is given below to help you to make the connections easily.

Since the module does not fit in a breadboard I have used the connecting wires directly to make the connections. Once the connection are made Arduino LoRa setup will look something like this below

pyLoRa for Raspberry Pi

There are many python packages that you can use with LoRa. Also commonly the Raspberry Pi is used as a LoRaWAN to get data from multiple LoRa nodes. But, in this project our aim to do Peer to Peer communication between two Raspberry Pi modules or between a Raspberry Pi and an Arduino. So, I decided to use the pyLoRa package. It has a rpsreal LoRa Arduino and rpsreal LoRa Raspberry pi modules which can be used on the Arduino and the Raspberry Pi environment. For now, let’s focus on the Raspberry Pi environment.

Configuring the Raspberry Pi for LoRa module

As told earlier the LoRa module works with SPI communication, so we have to enable SPI on Pi and then install the pylora package. Follow the below steps to do the same, after opening the terminal window of Pi. Again, I am using putty to connect to my Pi you can use your convenient method.

Step 1: Get into the configuration window using the following command. To get the below window

sudo raspi-config

Step 2: Navigate to interfacing options and enable SPI as shown in the image below. We have to enable the SPI interface because as we discussed the LCD and PI communicates through SPI protocol

Step 3: Save the changes and get back to the terminal window. Make sure pip and python is updated and then install the RPi.GPIO package using the following command.

pip install RPi.GPIO

This package class will help us control the GPIO pin on the Pi. If successfully installed your screen will look like this

Step 4: Similarly proceed with installing the spidev package using the following command. Spidev is a python binding for Linux which can be used to perform SPI communication on Raspberry Pi.

pip install spidev

If the installation is successful the terminal should look something like this below.

Step 5: Next lets install the pyLoRa package using the following pip command. This package installs the Radio models associated with LoRa.

pip install pyLoRa

If the installation is successful you will see the following screen.

The PyLoRa package also supports encrypted communication which can be used with Arduino and Raspberry Pi seamlessly. This will improve the data security in your communication. But you have to install separate package after this step which I am not doing since encryption is not in the scope of this tutorial. You can follow the above github links for more details.

After, this step you can add the package path information to pi and try with the python program given at the end. But I was not able to add the path successfully and hence had to manually download library and use the same directly for my programs. So I had to proceed with the following steps

Step 6: Download and install the python-rpi.gpio package and spidev package using the below command.

sudo apt-get install python-rpi.gpio python3-rpi.gpiosudo apt-get install python-spidev python3-spidev

The terminal window should display something like this after both the installations.

Step 7: Also install git and then use it to clone the python directory for our Raspberry Pi. You can do that using the following commands.

sudo apt-get install gitsudo git clone https://github.com/rpsreal/pySX127x

Once this step is complete you should find the SX127x sub directory in Raspberry Pi home folder. This will have all the required files associated with the library.

Programming Raspberry Pi for LoRa

In a peer to peer LoRa communication the module that is transmitting the information is called a server and the module that receives the information is called a client. In most cases the Arduino will be used in the field with a sensor to measure data and the Pi will be used to receive these data. So, I decided to use the Raspberry Pi as a client and the Arduino as a server in this tutorial. The complete Raspberry Pi client program can be found at the bottom of this page. Here I will try to explain the important lines in the program.

Caution: Make sure the program file is in the same directory where the SX127x library folder is present. You can copy this folder and use it anywhere if you wish to port the project.

The program is pretty simple we have to set the LoRa module to work in 433Mhz and then listen for incoming packets. If we receive anything we simple print them on the console. As always we begin the program by importing the required the python libraries.

from time import sleepfrom SX127x.LoRa import *from SX127x.board_config import BOARDBOARD.setup()

In this case the time package is used to create delays, the Lora package is used for LoRa communication and the board_config is used to set the board and LoRa parameters. We also setup the board using the BOARD.setup() function.

Next we create the python LoRa class with three definitions. Since we only indent to make the program work as a raspberry client the class has only three functions namely the init class, start class and on_rx_done class. The init class initializes the LoRa module in 433MHz with 125kHz bandwidth as set in the set_pa_config method. Then it also puts the module in sleep mode to save power consumption.

# Medium Range Defaults after init are 434.0MHz, Bw = 125 kHz, Cr = 4/5, Sf = 128chips/symbol, CRC on 13 dBmlora.set_pa_config(pa_select=1) def __init__(self, verbose=False): super(LoRaRcvCont, self).__init__(verbose) self.set_mode(MODE.SLEEP) self.set_dio_mapping([0] * 6)

The start function is where we configure the module as receiver and obtain like RSSI (Receiving signal strength Indicator), status, operating frequency etc. We set the module to work in continuous receiver mode (RXCONT) from sleep mode and then use a while loop to read values like RSSI and modem status. We also flush the data in the serial buffer onto the terminal.

def start(self): self.reset_ptr_rx() self.set_mode(MODE.RXCONT) while True: sleep(.5) rssi_value = self.get_rssi_value() status = self.get_modem_status() sys.stdout.flush()

Finally the on_rx_done function gets executed after the incoming packet is read. In this function the received values is moved into a variable called payload from the Rx buffer after setting the receiving flag high. Then the received values are decoded with utf-8 to print a user readable data on the shell. We also put the module back in sleep mode till another value is received.

def on_rx_done(self): print("\nReceived: ") self.clear_irq_flags(RxDone=1) payload = self.read_payload(nocheck=True) print(bytes(payload).decode("utf-8",'ignore')) self.set_mode(MODE.SLEEP) self.reset_ptr_rx() self.set_mode(MODE.RXCONT)

The remaining part of the program is just to print the received values on the console and terminate the program using a keyboard interrupt. We again set the board in sleep mode even after termination of the program to save power.

try: lora.start() except KeyboardInterrupt: sys.stdout.flush() print("") sys.stderr.write("KeyboardInterrupt\n") finally: sys.stdout.flush() print("") lora.set_mode(MODE.SLEEP) BOARD.teardown()

Arduino Code for LoRa to communicate with Raspberry Pi

As I mentioned earlier the code supports both Arduino and Pi and hence communication between Arduino and Pi is possible. It works based on the Radiohead Library from AirSpayce’s. So you have to install the radio head library first to your Arduino IDE.

To do that visit the Github page and download the library in ZIP folder. Then place it in the library folder of your Arduino IDE. Now, restart the Arduino IDE and you will find example files for Radio head library. Here we will program the Arduino to work as a LoRa server to send test packets like 0 to 9. The Complete code to do the same can be found at the bottom of this page as always. Here, I will explain few important lines in the program.

We begin the program by importing the SPI library (installed by default) to use SPI protocol and then the RH_RF95 library from Radio head to perform LoRa communication. Then we define to which pin of Arduino we have connected the Chip select (CS), Reset (RST) and Interrupt (INT) pin of the LoRa with Arduino. Finally we also define that the module should work in 434MHz Frequency and initialize the LoRa module.

#include <SPI.h> //Import SPI librarey#include <RH_RF95.h> // RF95 from RadioHead Librarey#define RFM95_CS 10 //CS if Lora connected to pin 10#define RFM95_RST 9 //RST of Lora connected to pin 9#define RFM95_INT 2 //INT of Lora connected to pin 2// Change to 434.0 or other frequency, must match RX's freq!#define RF95_FREQ 434.0// Singleton instance of the radio driverRH_RF95 rf95(RFM95_CS, RFM95_INT);

Inside the setup function we will reset the LoRa module by pulling its reset pin to low for 10 milli second to start fresh. Then we initialize it with the module that we created earlier using Radio head library. Then, we set the frequency and transmission power for the LoRa server. Higher the transmission more distance your packets will travel but will consume more power.

void setup(){//Initialize Serial Monitor Serial.begin(9600);// Reset LoRa Module pinMode(RFM95_RST, OUTPUT); digitalWrite(RFM95_RST, LOW); delay(10); digitalWrite(RFM95_RST, HIGH); delay(10);//Initialize LoRa Module while (!rf95.init()) { Serial.println("LoRa radio init failed"); while (1); } //Set the default frequency 434.0MHz if (!rf95.setFrequency(RF95_FREQ)) { Serial.println("setFrequency failed"); while (1); } rf95.setTxPower(18); //Transmission power of the Lora Module}

Inside the infinite loop function, we simply have to send the data packet through the LoRa module. This data can be anything like sensor value of user command. But for simplicity we will send char value 0 to 9 for every 1 second interval and then initialize the value back to 0 after reaching 9. Note that the values can be sent only in a char array format and the type of data should be unit8_t that is 1 byte at a time. The code to do the same is shown below

void loop(){ Serial.print("Send: "); char radiopacket[1] = char(value)}; rf95.send((uint8_t *)radiopacket, 1); delay(1000); value++; if (value > '9') value = 48;}

Testing LoRa Communication between Raspberry Pi and Arduino

Now, that we got both our hardware and program ready we simply have to upload the Arduino code to the UNO board and the python sketch should be launched on pi. My test set-up with both the hardware connected, looks something like this below

Once the python client sketch is launched on the Pi (use only python 3), if everything is working properly you should see the Arduino packets received in pi though the shell window. You should notice “Received: 0” to 9 like shown in the image below.

The complete Raspberry pi code with all the required libraries can be downloaded from here.

You can now move the Arduino server and check the range of the module; it is also possible to display the RSSI value on the shell if required. The complete working of the project can be found in the video linked below. Now, that we know how to establish long distance low power LoRa communication between Arduino and Raspberry pi we can proceed with adding sensor on Arduino side and cloud platform on Pi side to make a complete IoT package.

Hope you understood the project and enjoyed building it. If you have problem in getting it to work, use the comment section below or the forums for other technical quires.

Originally published at https://circuitdigest.com on May 7, 2019.