🛠 LoRa point à point sans réseau (dumb modem)

Objectives

Use the Murata module in "dumb modem" mode: output the AT LoRaWAN firmware and directly control the SX1276 over SPI1, without a gateway or server. Two cards exchange messages in pure LoRa. Requires the arduino-LoRa library ≥ 0.5.0, which knows the MKR WAN 1300/1310 pinout (CS = LORA_IRQ_DUMB on SPI1).

Hardware

• 2 MKR WAN 1310 cards with antennas (433/868/915 MHz)
• Libraries: arduino-LoRa ≥ 0.5.0 (and MKRWAN for dumb mode)
• Micro-USB cables for both cards

Complete code

// ===== EMETTEUR =====
#include <SPI.h>
#include <LoRa.h>

int compteur = 0;
void setup {
  Serial.begin(9600);
  while (!Serial);
  // arduino-LoRa >= 0.5.0 redémarre le module Murata en mode bête lui-même
  if (!LoRa.begin(868E6)) {          // 868E6 (UE), 915E6 (US), 433E6
    Serial.println("Demarrage LoRa impossible");
    while (1);
  }
  Serial.println("LoRa emetteur pret");
}
void loop {
  LoRa.beginPacket;
  LoRa.print("bonjour ");
  LoRa.print(compteur++);
  LoRa.endPacket;                  // pas d'ACK en mode brut
  delay(5000);
}

// ===== RECEPTEUR (autre carte) =====
// meme setup ; dans loop :
// int taille = LoRa.parsePacket;
// if (taille) { while (LoRa.available)
//   Serial.write(LoRa.read); Serial.println; }

Expected verification

The transmitter increments a counter every 5 s; the receiver displays "hello N" with a delay of at most one packet. The range far exceeds Wi-Fi: a few km in the city, 16+ km in line of sight according to LoRa documentation.

Common errors

• Different frequencies between the two cards: no packet received, even if both display "ready".
• The module does not have a wired IRQ pin: the receiver must poll LoRa.parsePacket in a loop, not wait for an interrupt.
• Staying in AT mode: if an MKRWAN sketch ran before, re-upload the LoRa sketch which restarts the module in dumb mode.
• Different LoRa settings (spreading factor, bandwidth) between transmitter and receiver: arduino-LoRa uses identical default values, do not modify them on only one side.
• In raw mode, there is no retransmission or ACK: plan for an application-level acknowledgment if reliability matters.