IoT-Based Single-Phase Smart Energy Meter Using Dual-Core Edge Processing

A Dual-Core FreeRTOS-based single-phase smart energy meter built on the ESP32.

Overview

This project continuously tracks power consumption parameters such as Voltage, Current, Real Power, Power Factor, and Accumulated Energy using high-speed DMA-based ADC sampling and 64-bit DSP computations on Core 1 of the ESP32. Meanwhile, Core 0 manages Wi-Fi communication and synchronizes telemetry data with the Blynk IoT Cloud, enabling real-time monitoring, visualization, and continuous energy data storage.

Key Features

• Dual-Core Architecture: Segregates heavy math calculations from IoT networking to ensure reliable and uninterrupted sampling.
• High-Frequency DMA Sampling: Reads raw voltage and current data at 20kHz via hardware DMA.
• DSP Math & Phase Correction: Real-time calculation of RMS Voltage, RMS Current, Real Power, and Power Factor with hybrid phase correction for improved accuracy.
• Blynk IoT Integration: Live data streaming to the Blynk app/dashboard, including cloud-persisted energy accumulation.
• Push Notifications: Automatic alerts triggered for high power usage and energy thresholds.

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Wiring Guide

Hardware Required

• ESP32 Development Board
• ZMPT101B AC Voltage Sensor Module
• ACS712 AC Current Sensor Module
• AC Load and Power Source

Pin Mapping

The project uses the ESP32's ADC1 channels for continuous DMA sampling.

Component	ESP32 Pin	ADC Channel	Function
ZMPT101B (Voltage)	GPIO 32	ADC1_CHANNEL_4	Measures AC Voltage
ACS712 (Current)	GPIO 33	ADC1_CHANNEL_5	Measures AC Current

Important Safety Warning

DANGER: This project involves working with mains AC voltage (110V/220V), which can be lethal.

• Ensure all AC wiring is securely insulated and enclosed.
• Never touch the circuit while it is plugged into the wall.
• Ensure the ZMPT101B and ACS712 modules are correctly isolated.

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Implementation Details

The firmware utilizes ESP-IDF/FreeRTOS running within the Arduino core. The workload is strictly partitioned between the two ESP32 cores to achieve accurate, uninterrupted power measurements.

Core 1 (APP_CPU): DSP & Math Task

• DMA ADC: The adc_continuous API is configured to read from GPIO 32 and GPIO 33 at a sample rate of 20kHz (10k per channel).
• DSP Math: As the DMA buffer fills, Core 1 processes the data chunks (200ms windows). It squares the samples and multiplies voltage by current to calculate the vRms, iRms, realP (Real Power), and pf (Power Factor).
• Phase Correction: A hybrid phase correction mechanism consisting of a macro-shift (array indexing offset) and micro-shift (fractional interpolation) aligns the voltage and current waveforms to mitigate hardware-induced phase delays.
• IPC (Inter-Process Communication): Once a 200ms calculation is complete, the results are packaged into a struct and pushed to a FreeRTOS Queue.

Core 0 (PRO_CPU): IoT & Network Task

• Blynk Cloud: Connects to the local Wi-Fi and authenticates with the Blynk Cloud.
• Data Consumption: Reads the calculated data from the FreeRTOS Queue.
• Energy Accumulation: Accumulates Total Energy (Wh) and syncs the value with the Blynk server (Virtual Pin V5) to ensure it survives reboots.
• Telemetry: Pushes telemetry data (V, I, W, PF) to the Blynk dashboard every 2 seconds.
• Alerts: Evaluates power thresholds (e.g., >80W limit) and triggers push notifications through Blynk.

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Setup & Configuration

1. Prerequisites

• ESP32 Development Board.
• Arduino IDE or PlatformIO installed.
• ESP32 board package installed in your IDE.
• Blynk IoT App (iOS/Android) and an active account.

2. Library Dependencies

Make sure the following libraries are installed:

• WiFi.h (Built-in)
• BlynkSimpleEsp32.h (Available via Library Manager)

3. Blynk Configuration

1. Create a new Template in the Blynk Web Console:
   • Name: Single Phase Smart Meter (or your preferred name)
   • Hardware: ESP32
   • Connection Type: WiFi
2. Create the following Datastreams (Virtual Pins):
   • V1: Voltage (Double)
   • V2: Current (Double)
   • V3: Power (Double)
   • V4: Power Factor (Double)
   • V5: Energy (Double)
3. Copy your Template ID, Template Name, and Auth Token.
4. Replace the credentials at the top of SinglePhase.ino:

   #define BLYNK_TEMPLATE_ID "Your_Template_ID"
   #define BLYNK_TEMPLATE_NAME "Your_Template_Name"
   #define BLYNK_AUTH_TOKEN "Your_Auth_Token"

4. Wi-Fi Configuration

Update your local Wi-Fi credentials in the code:

char ssid[] = "Your_WiFi_SSID";
char pass[] = "Your_WiFi_Password";

5. Calibration

The constants VCAL, ICAL, SAMPLE_SHIFT, and PHASECAL at the top of the file determine measurement accuracy. They are currently tuned for a 100W bulb at ~235V. To recalibrate:

1. Use a known resistive load (e.g., an incandescent bulb) and a multimeter.
2. Adjust VCAL so the serial output matches your multimeter's AC voltage reading.
3. Adjust ICAL so the serial output matches your multimeter's AC current reading.
4. Adjust PHASECAL and SAMPLE_SHIFT to ensure the Power Factor reads exactly 1.0 for a pure resistive load.

6. Flashing

Upload the code to your ESP32. Open the Serial Monitor (115200 baud) to view the DC Offset auto-calibration and real-time power data.