Current sensor

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Rogowski Coil–Based Current Sensor with Edge Connectivity

This project implements a non-invasive current measurement system based on a Rogowski coil, combined with embedded digital signal processing and wireless data transmission. The system measures peak current, RMS current, and frequency of an AC signal and publishes the results to an MQTT broker for real-time edge visualization.

The project demonstrates a complete cyber-physical system (CPS) pipeline, spanning analog sensing, bare-metal firmware, digital signal processing, wireless communication, and edge-side visualization.

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Key Features

• Non-invasive current sensing using a hand-wound Rogowski coil
• Wide bandwidth measurement without magnetic saturation
• Bare-metal firmware on ATmega328P (no Arduino / RTOS)
• Fixed-point FIR filtering and digital integration
• Peak, RMS, and frequency estimation
• Real-time OLED display (SSD1306)
• SPI communication between ATmega328P and ESP8266
• Wi-Fi + MQTT data publishing using ESP8266 (ESP_RTOS_SDK)
• Edge visualization using Python and Matplotlib

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visualization app

• edge_listener.py

System Architecture

Hardware Blocks

• Rogowski Coil + Signal Conditioning
  Produces a small voltage proportional to di/dt, followed by amplification and conditioning.

• ATmega328P (16 MHz)
  Performs ADC sampling, FIR filtering, digital integration, current calculation, frequency estimation, and display control.

• SSD1306 OLED (128×32, I²C)
  Displays peak current, RMS current, and frequency locally.

• ESP8266
  Acts as an SPI slave, connects to Wi-Fi, and publishes data via MQTT.

• Edge Device (PC)
  Subscribes to MQTT data and visualizes it in real time using Python.

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Firmware Overview

ATmega328P (Bare-Metal)

• Written in register-level C for deterministic behavior
• No Arduino framework or operating system
• Timer-driven ADC sampling at 1 kHz
• 31-tap FIR low-pass filter implemented using Q15 fixed-point arithmetic
• Digital integration using Forward Euler method
• Zero-crossing based frequency estimation
• SPI master for data transfer to ESP8266

Source files:

• main.c – System initialization and main loop
• adc.c / adc.h – ADC configuration and sampling
• timer.c / timer.h – Timer-based sampling control
• fir.c / fir.h – FIR filter implementation
• spi.c / spi.h – SPI communication with ESP8266
• i2c.c / i2c.h – I²C driver
• ssd1306.c / ssd1306.h – OLED driver

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ESP8266 (ESP_RTOS_SDK)

• Configured as SPI slave
• Receives current and frequency values from ATmega328P
• Connects to Wi-Fi network
• Publishes measurements via MQTT in JSON format