Modbus RTU Slave Monitor with RMS Sensor

Summary

Firmware for Modbus RTU slave device on ESP32 with ADS1015 ADC, calculates real-time RMS values using circular FIFOs, maintains measurement history and responds to Modbus RTU queries over RS485 within a FreeRTOS environment.

Dependencies

• FreeRTOS: tasks, queues, semaphores and synchronization.
• Arduino core ESP32 + Wire/I2C + ModbusServerRTU.
• Adafruit_ADS1X15 for ADC communication.
• PlatformIO as recommended toolchain.

Groups

• Hardware and System: pin configuration, peripherals and system initialization.
• ADC Processing and RMS Calculation: ADC acquisition, signal processing and RMS calculation with circular FIFOs.
• Modbus Communication: Modbus RTU server, registers and RS485 communication.

General Flow

1. Startup: setup() initializes Serial/I2C, ADS1015, ModbusServerRTU, queues and tasks.
2. ADC Configuration: sets gain, sampling rate and interrupt mode for ADS1015.
3. Acquisition: task_adquisicion manages round-robin conversions between channels using interrupts; queues samples in queue_adc_samples.
4. Processing: task_procesamiento consumes samples, updates circular FIFOs with cumulative sums and calculates RMS periodically using incremental algorithms.
5. History: RMS values are stored in thread-safe circular buffers protected by rms_history_mutex.
6. Modbus Update: dataUpdateTask extracts data from history, applies conversion factor and updates holdingRegisters.
7. Modbus Responses: readHoldingRegistersWorker handles read requests for configuration parameters (registers 0-7) and RMS data (registers 10+).
8. Debug: loop() displays RMS values periodically for system verification.

Queues and Synchronization

• queue_adc_samples: bridge acquisition → processing of ADC samples.
• fifos[NUM_CHANNELS]: circular buffers for efficient RMS calculation.
• rms_history_ch0/ch1/ch2: independent histories for each channel.
• holdingRegisters: Modbus registers updated periodically.
• rms_history_mutex and dataMutex: critical synchronization for concurrent access.

Modbus Interface

• Registers 0-7: sensor configuration parameters (sensorID, numberOfChannels, startAddress, etc.).
• Registers 10+: historical RMS data organized by channel with applied conversion factor.
• Function 03: holding register read with address validation and error handling.
• Discovery: responds with SensorData structure for automatic identification by masters.

RMS Algorithm

• Circular FIFO: 320-sample buffer with cumulative sums for efficiency.
• Incremental calculation: mean and variance calculated without traversing entire buffer.
• Periodic update: RMS values calculated every 1000ms.
• Thread-safe: protected access through semaphores for safe concurrency.