LoRa weather station with acknowledgments on an Arduino Uno

// LoRa weather station, the sensor node: a BME280 read every 5 seconds and
// sent over an SX1278 (Ra-02) LoRa module to the gateway with RadioHead's
// RHReliableDatagram. The gateway acknowledges every reading; with no
// acknowledgment the library sends again, up to 3 retries, and the sketch
// says so if all of them go unanswered.
//
//   Ra-02     NSS -> 10   DIO0 -> 2   RST -> 9   SCK -> 13   MOSI -> 11
//             MISO -> 12   3.3V -> 3.3V   GND -> GND
//   BME280    SDA -> A4   SCL -> A5   VIN -> 5V   GND -> GND
//
// The SX1278 runs on 3.3 V and its pins are not 5 V tolerant: on the bench,
// put a level shifter on NSS, SCK, MOSI and RST, or use a 3.3 V board.
//
// Things to try. Drag the BME280's sliders. Hold the gateway's reset button
// and watch the retries run out. Change INTERVAL_MS for slower reports,
// which a battery node would use.

#include <SPI.h>
#include <RH_RF95.h>
#include <RHReliableDatagram.h>
#include <Wire.h>
#include <Adafruit_BME280.h>

const uint8_t NODE_ADDRESS = 1;
const uint8_t GATEWAY_ADDRESS = 2;
const float FREQUENCY = 433.0;  // MHz: the Ra-02 is a 433 MHz module
const unsigned long INTERVAL_MS = 5000;
const uint8_t RESET_PIN = 9;

RH_RF95 rf95(10, 2);  // NSS, DIO0
RHReliableDatagram manager(rf95, NODE_ADDRESS);
Adafruit_BME280 bme;

// What goes on the air: 8 bytes, the same layout on both boards.
struct __attribute__((packed)) Reading {
  int16_t centiC;        // temperature, hundredths of a degree C
  uint16_t deciHum;      // humidity, tenths of a percent
  uint16_t deciHpa;      // pressure, tenths of a hectopascal
  uint16_t count;
};

uint16_t count = 0;
unsigned long lastSent = 0;

void setup() {
  Serial.begin(9600);
  // Reset the radio, as the module's datasheet asks, before talking to it.
  pinMode(RESET_PIN, OUTPUT);
  digitalWrite(RESET_PIN, LOW);
  delay(10);
  digitalWrite(RESET_PIN, HIGH);
  delay(10);

  if (!bme.begin(0x76)) {
    Serial.println("no BME280 at 0x76: check SDA and SCL");
    while (1) {}
  }
  if (!manager.init()) {
    Serial.println("LoRa radio not found: check NSS, DIO0 and the 3.3 V supply");
    while (1) {}
  }
  rf95.setFrequency(FREQUENCY);
  rf95.setTxPower(13);
  manager.setRetries(3);
  manager.setTimeout(500);  // ms to wait for an acknowledgment
  Serial.println("LoRa weather node 1 ready");
}

void loop() {
  if (millis() - lastSent < INTERVAL_MS && lastSent != 0) return;
  lastSent = millis();

  float t = bme.readTemperature();
  float h = bme.readHumidity();
  float p = bme.readPressure() / 100.0;
  Reading r = {(int16_t)lround(t * 100), (uint16_t)lround(h * 10), (uint16_t)lround(p * 10), ++count};

  Serial.print("reading ");
  Serial.print(count);
  Serial.print(": ");
  Serial.print(t, 1);
  Serial.print(" C, ");
  Serial.print(h, 0);
  Serial.print(" %, ");
  Serial.print(p, 1);
  Serial.print(" hPa: ");
  if (manager.sendtoWait((uint8_t *)&r, sizeof(r), GATEWAY_ADDRESS)) {
    Serial.println("acknowledged");
  } else {
    Serial.println("no acknowledgment after 3 retries");
  }
}

// LoRa weather station, the gateway: receives the sensor node's readings
// over an SX1278 (Ra-02) with RadioHead's RHReliableDatagram, acknowledges
// each one, and shows the latest on a 16x2 I2C LCD. Every reading also goes
// to the serial monitor with its RSSI, ready for a computer to log.
//
//   Ra-02     NSS -> 10   DIO0 -> 2   RST -> 9   SCK -> 13   MOSI -> 11
//             MISO -> 12   3.3V -> 3.3V   GND -> GND
//   LCD       SDA -> A4   SCL -> A5   VCC -> 5V   GND -> GND
//
// The SX1278 runs on 3.3 V and its pins are not 5 V tolerant: on the bench,
// put a level shifter on NSS, SCK, MOSI and RST, or use a 3.3 V board.
//
// Things to try. Change FREQUENCY here only and nothing arrives. Change
// STALE_MS to flag a quiet node sooner.

#include <SPI.h>
#include <RH_RF95.h>
#include <RHReliableDatagram.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const uint8_t GATEWAY_ADDRESS = 2;
const float FREQUENCY = 433.0;  // MHz, the same as the node
const unsigned long STALE_MS = 20000;
const uint8_t RESET_PIN = 9;

RH_RF95 rf95(10, 2);  // NSS, DIO0
RHReliableDatagram manager(rf95, GATEWAY_ADDRESS);
LiquidCrystal_I2C lcd(0x27, 16, 2);

struct __attribute__((packed)) Reading {
  int16_t centiC;
  uint16_t deciHum;
  uint16_t deciHpa;
  uint16_t count;
};

uint8_t buf[RH_RF95_MAX_MESSAGE_LEN];
unsigned long lastHeard = 0;
bool heard = false;
bool stale = false;

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  pinMode(RESET_PIN, OUTPUT);
  digitalWrite(RESET_PIN, LOW);
  delay(10);
  digitalWrite(RESET_PIN, HIGH);
  delay(10);
  if (!manager.init()) {
    Serial.println("LoRa radio not found: check NSS, DIO0 and the 3.3 V supply");
    lcd.print("No LoRa radio");
    while (1) {}
  }
  rf95.setFrequency(FREQUENCY);
  rf95.setTxPower(13);
  Serial.println("LoRa gateway listening");
  lcd.print("Waiting for node");
}

void loop() {
  uint8_t len = sizeof(buf);
  uint8_t from;
  // recvfromAck() sends the acknowledgment before it returns.
  if (manager.recvfromAck(buf, &len, &from)) {
    if (len != sizeof(Reading)) return;
    Reading r;
    memcpy(&r, buf, sizeof(r));
    heard = true;
    stale = false;
    lastHeard = millis();

    lcd.clear();
    lcd.print(r.centiC / 100.0, 1);
    lcd.print(" C  ");
    lcd.print(r.deciHum / 10.0, 0);
    lcd.print(" %");
    lcd.setCursor(0, 1);
    lcd.print(r.deciHpa / 10.0, 1);
    lcd.print(" hPa");

    Serial.print("node ");
    Serial.print(from);
    Serial.print(" #");
    Serial.print(r.count);
    Serial.print(": ");
    Serial.print(r.centiC / 100.0, 1);
    Serial.print(" C, ");
    Serial.print(r.deciHum / 10.0, 0);
    Serial.print(" %, ");
    Serial.print(r.deciHpa / 10.0, 1);
    Serial.print(" hPa, RSSI ");
    Serial.println(rf95.lastRssi());
  }

  if (heard && !stale && millis() - lastHeard > STALE_MS) {
    stale = true;
    lcd.setCursor(0, 1);
    lcd.print("node quiet 20 s ");
    Serial.println("no reading for 20 s");
  }
}