LoRa Long-Range Sensor Link

Overview

LoRa trades speed for range: a few bytes a minute can travel 1–2 km in a city and much further with line of sight. That's perfect for a farm, a rooftop tank, a villa garden or a remote gate where Wi-Fi doesn't reach.

The sender is an ET-M09 ESP32-C3 battery board with an ET-S61 temperature/humidity sensor and an ET-C15 LoRa radio. It wakes once a minute, sends one packet with the readings and its battery voltage, and sleeps. The receiver — an ET-M02 with a second ET-C15 — prints each packet with its signal strength.

• 1–2 km range in town, more in open country
• Temperature, humidity and sender battery voltage
• Signal strength (RSSI) and SNR for every packet
• Sender runs for weeks on a LiPo

What you need

ElectroTrical boards

ET-C15 × 2LoRa 433 MHz BoardOne radio at each end

Coming soon

ET-M09ESP32-C3 Battery Dev BoardSender: LiPo charger and battery monitor built in

Coming soon

ET-S61AHT20 Temperature + Humidity SensorSensor at the remote end

Coming soon

ET-M02ESP32-S3 Dev BoardReceiver

Coming soon

You'll also need

• 1S LiPo, 1,000–2,000 mAh with JST-PH connector, for the sender
• 1 Qwiic cable
• Jumper wires
• Weatherproof box for the sender

Wiring

Never power a LoRa radio without its antenna fitted — transmitting into nothing can damage it. 433 MHz is a short-range-device band in the UAE and many countries; keep to the default power and check your local rules.

Build it

1. 01

   Fit the antennas

   Screw the spring antennas onto both ET-C15 boards and keep them vertical. Range depends far more on antenna height than on anything in the code.

2. 02

   Wire both ends

   Wire the sender and receiver as in the tables. The ESP32-C3 pins are chosen to avoid its boot-strap pins (IO2, IO8, IO9).

3. 03

   Set up the Arduino IDE

   Install the Espressif ESP32 package. For the sender select “ESP32C3 Dev Module”, for the receiver “ESP32S3 Dev Module”; set USB CDC On Boot to Enabled for both.

4. 04

   Upload the two sketches

   Upload the receiver part to the ET-M02 and open Serial Monitor. Upload the sender part to the ET-M09. A packet should appear within a minute.

5. 05

   Range test

   Run the sender on battery and walk away with the receiver on a laptop. RSSI around −120 dBm is the edge of reliable reception at these settings.

6. 06

   Deploy

   Mount the sender box as high as possible with the antenna pointing up, out of direct sun.

Arduino code

Written for the ET-M09 ESP32-C3 Battery Dev Board (sender) and ET-M02 ESP32-S3 Dev Board (receiver). Install these libraries from the Arduino Library Manager:

• LoRa by Sandeep Mistry
• Adafruit AHTX0

// ===================== SENDER (ET-M09, ESP32-C3) =====================
#include <SPI.h>
#include <Wire.h>
#include <LoRa.h>
#include <Adafruit_AHTX0.h>

const int SCK_PIN = 4, MISO_PIN = 5, MOSI_PIN = 3, CS_PIN = 1, RST_PIN = 20, DIO0_PIN = 21;
const int BATT_PIN = 0;             // battery / 2 on IO0
const int SLEEP_S = 60;

Adafruit_AHTX0 aht;

void setup() {
  Serial.begin(115200);
  Wire.begin(6, 7);
  aht.begin();

  SPI.begin(SCK_PIN, MISO_PIN, MOSI_PIN, CS_PIN);
  LoRa.setPins(CS_PIN, RST_PIN, DIO0_PIN);
  if (!LoRa.begin(433E6)) { Serial.println("LoRa not found"); esp_deep_sleep(10e6); }
  LoRa.setSpreadingFactor(9);
  LoRa.setTxPower(14);
  LoRa.enableCrc();

  sensors_event_t hum, temp;
  aht.getEvent(&hum, &temp);
  float vbat = analogReadMilliVolts(BATT_PIN) * 2 / 1000.0;

  char msg[48];
  snprintf(msg, sizeof msg, "T=%.1f,H=%.0f,B=%.2f", temp.temperature, hum.relative_humidity, vbat);
  LoRa.beginPacket();
  LoRa.print(msg);
  LoRa.endPacket();
  LoRa.sleep();
  Serial.println(msg);

  esp_deep_sleep((uint64_t)SLEEP_S * 1000000ULL);
}
void loop() {}

// ===================== RECEIVER (ET-M02, ESP32-S3) ===================
// Save this half as its own sketch.
/*
#include <SPI.h>
#include <LoRa.h>

void setup() {
  Serial.begin(115200);
  SPI.begin(12, 13, 11, 10);        // SCK, MISO, MOSI, CS
  LoRa.setPins(10, 4, 5);           // CS, RST, DIO0
  if (!LoRa.begin(433E6)) { Serial.println("LoRa not found"); while (1) delay(100); }
  LoRa.setSpreadingFactor(9);       // must match the sender
  LoRa.enableCrc();
  Serial.println("Listening on 433 MHz...");
}

void loop() {
  if (LoRa.parsePacket()) {
    String msg = LoRa.readString();
    Serial.printf("%s | RSSI %d dBm | SNR %.1f dB\n", msg.c_str(), LoRa.packetRssi(), LoRa.packetSnr());
  }
}
*/

Troubleshooting

Take it further

• Forward packets to Home Assistant or a web dashboard from the receiver over Wi-Fi
• Add a water-level or soil sensor to the remote node
• Use the ET-P19 timer to cut the sender's sleep current to nanoamps