Multiple LoRa Device Communication

In this part of my LoRa Series ( Part 3 ) I will look at some basic code for the Heltec LoRa 32 V2 Module. This code will in particular be focused on Multiple device communication. It can easily adapted from the stock example (as provided below) to implement a custom addressing scheme.

LoRa Multiple Communications No Interrupt

#include "heltec.h"

#define BAND    433E6  //you can set band here directly,e.g. //868E6,915E6


String outgoing;              // outgoing message

byte localAddress = 0xBB;     // address of this device
byte destination = 0xFD;      // destination to send to

byte msgCount = 0;            // count of outgoing messages
long lastSendTime = 0;        // last send time
int interval = 2000;          // interval between sends

void setup()
{
   //WIFI Kit series V1 not support Vext control
  Heltec.begin(true /*DisplayEnable Enable*/, true /*Heltec.LoRa Enable*/, true /*Serial Enable*/, true /*PABOOST Enable*/, BAND /*long BAND*/);

  Serial.println("Heltec.LoRa Duplex");

 
}

void loop()
{
  if (millis() - lastSendTime > interval)
  {
    String message = "Hello there!";   // send a message
    sendMessage(message);
    Serial.println("Sending " + message);
    lastSendTime = millis();            // timestamp the message
    interval = random(2000) + 1000;    // 2-3 seconds
  }

  // parse for a packet, and call onReceive with the result:
  onReceive(LoRa.parsePacket());
}

void sendMessage(String outgoing)
{
  LoRa.beginPacket();                   // start packet
  LoRa.write(destination);              // add destination address
  LoRa.write(localAddress);             // add sender address
  LoRa.write(msgCount);                 // add message ID
  LoRa.write(outgoing.length());        // add payload length
  LoRa.print(outgoing);                 // add payload
  LoRa.endPacket();                     // finish packet and send it
  msgCount++;                           // increment message ID
}

void onReceive(int packetSize)
{
  if (packetSize == 0) return;          // if there's no packet, return

  // read packet header bytes:
  int recipient = LoRa.read();          // recipient address
  byte sender = LoRa.read();            // sender address
  byte incomingMsgId = LoRa.read();     // incoming msg ID
  byte incomingLength = LoRa.read();    // incoming msg length

  String incoming = "";

  while (LoRa.available())
  {
    incoming += (char)LoRa.read();
  }

  if (incomingLength != incoming.length())
  {   // check length for error
    Serial.println("error: message length does not match length");
    return;                             // skip rest of function
  }

  // if the recipient isn't this device or broadcast,
  if (recipient != localAddress && recipient != 0xFF) {
    Serial.println("This message is not for me.");
    return;                             // skip rest of function
  }

  // if message is for this device, or broadcast, print details:
  Serial.println("Received from: 0x" + String(sender, HEX));
  Serial.println("Sent to: 0x" + String(recipient, HEX));
  Serial.println("Message ID: " + String(incomingMsgId));
  Serial.println("Message length: " + String(incomingLength));
  Serial.println("Message: " + incoming);
  Serial.println("RSSI: " + String(LoRa.packetRssi()));
  Serial.println();
}

LoRa Multiple communication, Interrupt

#include "heltec.h"

#define BAND    433E6  //you can set band here directly,e.g. 868E6,915E6

  
byte localAddress = 0xBB;     // address of this device
byte destination = 0xFF;      // destination to send to

String outgoing;              // outgoing message
byte msgCount = 0;            // count of outgoing messages
long lastSendTime = 0;        // last send time
int interval = 2000;          // interval between sends

void setup()
{
   //WIFI Kit series V1 not support Vext control
  Heltec.begin(true /*DisplayEnable Enable*/, true /*Heltec.LoRa Disable*/, true /*Serial Enable*/, true /*PABOOST Enable*/, BAND /*long BAND*/);

  LoRa.onReceive(onReceive);
  LoRa.receive();
  Serial.println("Heltec.LoRa init succeeded.");
}

void loop()
{
  if (millis() - lastSendTime > interval)
  {
    String message = "Hello World!";   // send a message
    sendMessage(message);
    Serial.println("Sending " + message);
    lastSendTime = millis();            // timestamp the message
    interval = random(2000) + 1000;     // 2-3 seconds
    LoRa.receive();                     // go back into receive mode
  }
}

void sendMessage(String outgoing)
{
  LoRa.beginPacket();                   // start packet
  LoRa.write(destination);              // add destination address
  LoRa.write(localAddress);             // add sender address
  LoRa.write(msgCount);                 // add message ID
  LoRa.write(outgoing.length());        // add payload length
  LoRa.print(outgoing);                 // add payload
  LoRa.endPacket();                     // finish packet and send it
  msgCount++;                           // increment message ID
}

void onReceive(int packetSize)
{
  if (packetSize == 0) return;          // if there's no packet, return

  // read packet header bytes:
  int recipient = LoRa.read();          // recipient address
  byte sender = LoRa.read();            // sender address
  byte incomingMsgId = LoRa.read();     // incoming msg ID
  byte incomingLength = LoRa.read();    // incoming msg length

  String incoming = "";                 // payload of packet

  while (LoRa.available())             // can't use readString() in callback
  {
    incoming += (char)LoRa.read();      // add bytes one by one
  }

  if (incomingLength != incoming.length())   // check length for error
  {
    Serial.println("error: message length does not match length");
    return;                             // skip rest of function
  }

  // if the recipient isn't this device or broadcast,
  if (recipient != localAddress && recipient != 0xFF)
  {
    Serial.println("This message is not for me.");
    return;                             // skip rest of function
  }

  // if message is for this device, or broadcast, print details:
  Serial.println("Received from: 0x" + String(sender, HEX));
  Serial.println("Sent to: 0x" + String(recipient, HEX));
  Serial.println("Message ID: " + String(incomingMsgId));
  Serial.println("Message length: " + String(incomingLength));
  Serial.println("Message: " + incoming);
  Serial.println("RSSI: " + String(LoRa.packetRssi()));
  Serial.println();
}

LoRa – Part 2

So many people asked me which Lora Module I use for my projects. In this part of the series, I will show you, as well as shed some light on another module, that although seemingly cheap, is, unfortunately, according to me, a complete waste of time and money.

Heltec LoRa 32 v 2 – The good stuff ( according to me at least)

Technical Specs
Electrical Specifications
Pinout

Installation in Arduino IDE:

Installation of the libraries into the Arduino IDE is quite easy, just follow the link to heltec…

The Bad ( according to me )

The following module, is, according to me, an absolute waste of time and money. Documentation is impossible to find, and that that you do find, as often incorrect. The pin-outs are wrong, with no definite standard.

I am talking about the TTGO Lora V1 or V2 or what ever ??? can seem to even find that answer reliably. I was initially attracted to this module, as it was allegedly compatible with the heltec version, and did not have the oled screen, which, to be honest, is not always needed in every project. It was also about 25% cheaper, and could be sourced locally, without enriching the greedy shipping companies 😉 (I just have to rant about this, as 25USD to ship 100g worth of stuff is a ripoff. Either that or 60 to 90 days of guess-if-it-will-arrive mail is not on ( and even that is 10 USD!)

So, having high hopes, I ordered one of these boards, hoping to use it together with my heltec boards… It arrived, and that was well the top came of.. I could immediately see that the quality of the PCB was quite bad. Documentation was missing, and even the supplier sent me to a heltec pinout, which, after a quick test were definitely not correct…

Google turned up mixed results, and eventually I found a sort of accurate pinout …

Alleged pinout for TTGO LoRa device

This pinout also turned out to be only about 50% correct, and after manually trying to map out the pins, I was sort of confident enough to test it further…

Further problems arose, LoRa does not work, I2C does not work, SPI does not work shall I continue…? 🙂 It now seems clear that the board that I bought was a clone of a clone, and a very bad one at that …
I will post a picture of the actual board below, in the interest of education, to inform others not to get duped as well. Likewise, If I am the mistaken party, and you have had success with this board, please give me a message/yell and lets share some knowledge

The Front (Top Side) of the Module

Front (Top) of the module
Back (Bottom) of the module

I hope that you found this useful and that I will see you for part 3 of the series, where I will get into the actual coding.

What is LoRa?

Introduction

When designing IoT solutions, we all encounter the problem of connecting our device(s) to each other, either directly, or through the internet. In Urban areas, it is quite easy to use WiFi or even GSM to achieve this, but these solutions often come with additional costs in the form of subscriptions. Although it is possible to run your own WiFi network free of charge, you will soon run into issues with the range…

Enter LoRa (short for Long Range) Radio communication. LoRa is a radio technology derived from chirp spread spectrum technology. It uses an ISM band, meaning it is unregulated in most countries, if you use the correct frequency for your country, that is.

It is also extremely low power, making it ideal for use with battery-powered devices.
The technology is available in Node-to-Node, as well as Node-to -Gateway modes.

In this series, I will show you how to use a few of the existing LoRa Modules available on the market.

Ai-Tinker Ra-02 (Sx1278)

Ra-02 Lora Module, with spring antenna, by Ai-Tinker

This Module is conveniently broken-out onto a breakout board. It is sort of bread-board friendly (depending on the size of your bread-board) and is nicely labelled. It is also extremely cheap ( around $USD5 each, depending on where you buy from).

Caveats

There are quite a few important things that you should know about these modules before you start using them.

Disclaimer: The caveats listed below are by no means complete, or even valid. They are the result of experimentation by myself, with the intent to destroy a few modules, to see how hardy they are. Also take into mind, that living in SE Asia, it is quite common to buy something from a shop, where the seller has no or only a very limited idea of what he or she is selling, and are thus usually quite unable to provide any technical support.

To summarise: USE YOUR HEAD. If I did leave out something, it is quite possible that I forgot, or decided not to include it on purpose. This is a general guide, and you should ideally do your own research as well. That is the best way to learn.



1) Always connect an Antenna. This may seem like a logical one, but it is extremely important. The module is capable of quite a lot of transmission power, and operating it without an antenna will quickly damage the module, permanently.

2) ONLY use 3.3v, even on the control lines (the module uses SPI). This is quite important, as it is not very clearly stated by the suppliers, and will result in very short-lived component operation 😉 If you absolutely have to use 5v, use a level converter. (There are examples available on the internet, where they use this chip directly from an Arduino Uno. I can confirm that that approach does work, BUT, not for very long. I have purposely sacrificed a pair of transceiver modules so that you don’t have to. You can also adjust the SPI frequency, in the event that your level converter is not capable of running at a high SPI frequency.

3)Make sure that you connect ALL the ground pins on the device. This is another area that is not fully explained by the user manual and does “unexplainably” result in damaged modules.

4) Use short, good quality cables, and if possible, keep the module off the breadboard.
While testing the modules, I found that the usual DuPont wires, as everyone should know by now, are quite unreliable. Combine that with a bread-board that has seen its share of use,
and it is a definite recipe for headache 🙂

5) LoRa Antennas are polarised, make sure you have your antennas in the same orientation.
Although this will not prevent it from working over short distances, it makes sense to just do it correctly. Good RF practices never hurt anybody 🙂

Connecting to Arduino

A Note on Power:
It is important to power this module from a decent dedicated 3.3v power-supply.
The Arduino Uno does sometimes have a 3.3v regulator on-board. From my tests, it is however not always up to the task, as the module may spike up to 120mA when transmitting. It is thus also recommended to have a nice fat capacitor across the power lines (decoupling cap) to soak up any spikes.

As mentioned above, a level converter is mandatory for a 5v Arduino. You may do without it if you use a 3.3v Arduino, but once again, your mileage will vary 🙂

Both the transmitter and receiver uses the same connections, which are listed below:

LoRa SX1278 ModuleArduino Board
3.3V
GndGnd
En/NssD10
G0/DIO0D2
SCKD13
MISOD12
MOSID11
RSTD9
Connections to the Arduino from a LoRa RA-02 Module

Remember that you NEED a Level converter between the LoRa Module and the Arduino.

Software Library

The software library that we will use in our example is the excellent library from Sandeep Mistry. We will just include this into the Arduino IDE, and then use a slightly modified version of the examples for our experiment. It is also important to note that we will use Node-to Node communication, NOT LoRaWan. This means that all your communications will essentially be unencrypted, and not addressed. This does however allow you the flexibility to design and implement your own addressing scheme.

LORA code for Transmitting Side

#include <SPI.h>
#include <LoRa.h>

int counter = 0;

void setup() {
  Serial.begin(115200);
  while (!Serial);

  Serial.println("LoRa Sender");

  if (!LoRa.begin(433E6)) { // Set the frequency to that of your  //module. Mine uses 433Mhz, thus I have set it to 433E6
    Serial.println("Starting LoRa failed!");
    while (1);
  }

  LoRa.setTxPower(20);
  
}

void loop() {
  Serial.print("Sending packet: ");
  Serial.println(counter);

  // send packet
  LoRa.beginPacket();
  LoRa.print("hello ");
  LoRa.print(counter);
  LoRa.endPacket();

  counter++;

  delay(5000);
}
LORA code for Receiver Side

#include <SPI.h>
#include <LoRa.h>

void setup() {
  Serial.begin(115200);
  while (!Serial);

  Serial.println("LoRa Receiver");

  if (!LoRa.begin(433E6)) {
    Serial.println("Starting LoRa failed!");
    while (1);
  }
}

void loop() {
  // try to parse packet
  int packetSize = LoRa.parsePacket();
  if (packetSize) {
    // received a packet
    Serial.print("Received packet '");

    // read packet
    while (LoRa.available()) {
      Serial.print((char)LoRa.read());
    }

    // print RSSI of packet
    Serial.print("' with RSSI ");
    Serial.println(LoRa.packetRssi());
  }
}

Where to from here?

If all went well, you will see packets being received in the serial monitor of the Arduino IDE, connected to the receiver module. You will also see that the data from this example is sent as a string… It is however also possible to send binary data, by using the LoRa.write() function.

In the next part of this series, I will show you how to use LoRa with the ESP32/ESP8266,
as well as a working example with binary data transmission and an addressing scheme in part 3.

Thank you