STM32-Based Modbus RTU Soil TH/NPK and Environmental Monitor

Overview

This system is an industrial-grade environmental monitoring node designed to precisely measure soil health parameters in real time. Utilizing an STM32 microcontroller as the primary processing core, the system interfaces with an industrial multi-parameter soil probe via an RS485 physical layer. The firmware implements the Modbus RTU protocol to query and parse critical agronomic data—including Temperature, Humidity, pH, Nitrogen (N), Phosphorus (P), Potassium (K), Salinity, and Total Dissolved Solids (TDS)—for localized processing and data forwarding.

Key features

• STM32 core using UART + DMA for reliable high-rate polling and parsing.
• Custom Modbus RTU master: packet build/parse with CRC-16 generation and validation.
• TTL-to-RS485 transceiver for differential, noise-immune runs to the probe.
• Register map decoding for calibrated NPK, moisture, and chemical metrics.
• Power sequencing plus TVS protection on RS485 for outdoor transients and ground-loop stress.

Hardware integration

Dual-rail power: isolated high-voltage (5–30 V) field loop for the probe versus 3.3 V logic for the MCU and transceiver. A unified ground matrix ties domains to avoid floating RS485 receivers and common-mode corruption; level shifters guard MCU pins where needed. Bench validation used a scope and logic analyzer to verify UART timing, CRC integrity, and clean half-duplex direction changes on the RS485 transceiver.