LoRa Point-to-Point with ESP32 and SX1276: Sender, Receiver and ACK

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

const int PIN_NSS = 5, PIN_RST = 14, PIN_DIO0 = 26;
uint32_t counter = 0;

void radioConfig() {               // MUST match the receiver exactly
  LoRa.setSpreadingFactor(9);
  LoRa.setSignalBandwidth(125E3);
  LoRa.setCodingRate4(5);
  LoRa.setSyncWord(0xF3);
  LoRa.setTxPower(14);             // dBm, PA_BOOST output
  LoRa.enableCrc();                // drop corrupted packets
}

void setup() {
  Serial.begin(115200);
  LoRa.setPins(PIN_NSS, PIN_RST, PIN_DIO0);
  if (!LoRa.begin(866E6)) {        // frequency in Hz
    Serial.println("LoRa init failed, check wiring");
    while (true) delay(1000);
  }
  radioConfig();
  Serial.println("Sender ready");
}

bool waitForAck(uint32_t id, uint32_t timeoutMs) {
  uint32_t start = millis();
  while (millis() - start < timeoutMs) {
    if (LoRa.parsePacket()) {      // returns packet size, 0 if none
      String reply;
      while (LoRa.available()) reply += (char)LoRa.read();
      if (reply == "ACK:" + String(id)) return true;
    }
  }
  return false;
}

void loop() {
  float tankLevel = analogRead(34) * 100.0 / 4095;  // demo sensor, percent
  String msg = "N1," + String(counter) + "," + String(tankLevel, 1);

  bool ok = false;
  for (int attempt = 1; attempt <= 3 && !ok; attempt++) {
    LoRa.beginPacket();
    LoRa.print(msg);
    LoRa.endPacket();              // blocks until transmission ends
    ok = waitForAck(counter, 1000);
    Serial.printf("Sent %s, attempt %d, %s", msg.c_str(), attempt, ok ? "ACK" : "no ACK");
    Serial.println();
  }
  counter++;
  delay(10000);
}

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

const int PIN_NSS = 5, PIN_RST = 14, PIN_DIO0 = 26;

void radioConfig() {               // identical to the sender
  LoRa.setSpreadingFactor(9);
  LoRa.setSignalBandwidth(125E3);
  LoRa.setCodingRate4(5);
  LoRa.setSyncWord(0xF3);
  LoRa.setTxPower(14);
  LoRa.enableCrc();
}

void setup() {
  Serial.begin(115200);
  LoRa.setPins(PIN_NSS, PIN_RST, PIN_DIO0);
  if (!LoRa.begin(866E6)) {
    Serial.println("LoRa init failed");
    while (true) delay(1000);
  }
  radioConfig();
  Serial.println("Receiver ready");
}

void loop() {
  int size = LoRa.parsePacket();
  if (size == 0) return;

  String msg;
  while (LoRa.available()) msg += (char)LoRa.read();
  int rssi = LoRa.packetRssi();    // dBm, closer to 0 is stronger
  float snr = LoRa.packetSnr();    // dB, can be negative for LoRa

  // Format: N1,<counter>,<value>
  int c1 = msg.indexOf(','), c2 = msg.indexOf(',', c1 + 1);
  if (c1 < 0 || c2 < 0) return;   // not our format
  String id = msg.substring(c1 + 1, c2);

  delay(50);                       // give the sender time to switch to RX
  LoRa.beginPacket();
  LoRa.print("ACK:" + id);
  LoRa.endPacket();

  Serial.printf("%s  RSSI %d dBm  SNR %.1f dB", msg.c_str(), rssi, snr);
  Serial.println();
}