The Connectivity Gap in the Field

Modern agriculture is increasingly reliant on data, yet the "last mile" of connectivity remains a significant hurdle. In large-scale farming or remote vineyards, traditional Wi-Fi is range-limited, and cellular data is often too expensive or unavailable. This project addresses the gap by utilizing LoRa (Long Range) technology to create a low-power, long-distance monitoring node capable of transmitting vital soil and atmospheric data over several kilometers.

By combining an ESP32 microcontroller with a Semtech SX1276 LoRa transceiver, this node can operate for months on a single LiPo battery, providing a cost-effective solution for precision irrigation and crop health monitoring.

The System Architecture

The node is designed around the ESP32-LoRa development board, which integrates the MCU and radio on a single PCB. The sensor suite includes a capacitive soil moisture sensor (to avoid the corrosion issues of resistive versions), a DHT22 for ambient temperature and humidity, and a BMP280 for barometric pressure.

Data is collected every 15 minutes. To conserve energy, the ESP32 utilizes its Deep Sleep mode, drawing only a few microamps between transmissions. The data is sent to a central gateway (such as a Dragino or a DIY Raspberry Pi gateway), which سپس pushes the information to an MQTT broker or a dashboard like ThingsBoard.

Bill of Materials (BOM)

To build this node, you will need the following components:

• Microcontroller: Heltec WiFi LoRa 32 (V2) or TTGO LoRa32.
• Soil Moisture Sensor: Capacitive Soil Moisture Sensor v1.2. Climate Sensor:
• DHT22 (High precision temperature and humidity). Pressure Sensor:
• BMP280 (I2C interface). Power: 3.7V 2000mAh LiPo Battery + 5V/6V Solar
• Panel. Enclosure: IP65 rated waterproof junction box. Antenna:
• 868MHz/915MHz SMA Antenna (matching your region's frequency).

Engineering Challenges: Power and Precision

One of the primary hurdles in remote sensing is power management. While the ESP32 is powerful, its Wi-Fi and Bluetooth stacks are energy-hungry. By disabling these radios and using the LoRa PHY layer exclusively, we significantly extend battery life. This project utilizes an external MOSFET to "gate" the power to the sensors, ensuring they are only powered during the 2-second measurement window.

Another challenge is sensor calibration. Capacitive soil sensors provide an analog voltage that varies based on soil density and mineral content. The project documentation includes a calibration script to map raw ADC values to "dry" and "wet" percentages.

External Resources & Code

The firmware is written in C++ using the Arduino framework, leveraging the LMIC (LoRaWAN-MAC-in-C) library for standardized communication.

• Firmware Repository: GitHub - LoRa-Agri-Node-Core (Placeholder link)
• Library Documentation: MCCI LoRaWAN LMIC Library
• Guides: The Things Network - LoRaWAN Frequencies by Country