High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino

Arduino project to measure mains/grid frequency and publish it as SSE and MQTT streams with display on an internal web server

This Arduino software allows you to measure the mains grid frequency (nominally 50 Hz) to high resolution (1 mHz) and display the frequency on a web page served from an internal web server.

This project is the result of various iterations of trying to build a simple device to measure mains frequency. So far this is the simplest hardware design, coupled with the most accurate software algorithm.

The algorithm samples a floating ADC input during 1 second, picking up the ambient mains 'hum'. While sampling, the measured waveform is correlated with a 'perfect' reference 50 Hz quadrature waveform. This gives an I and Q value from which the relative phase between the measured waveform and the reference waveform can be determined. Small frequency deviations in the actual mains waveform cause this phase to shift over time. From this shift, the instantaneous frequency of the measured waveform is derived each second.

The measured frequency values are published on /events as server-sent events (SSE). The internal web server serves a web page with javascript that connects an event source to this SSE stream. The instantaneous value is visualized as a gauge using canvas-gauges by Mykhailo Stadnyk.

The hardware consists of a Luatos ESP32-C3 board: https://wiki.luatos.org/chips/esp32c3/board.html

No connection to the mains is required. The mains signal is picked up from the ambient electric field of mains "hum" on an unconnected ADC input of the ESP chip.

This board was chosen because it is inexpensive, has a relatively stable and accurate clock crystal and has ADC inputs that are 'floating'.

Platformio will install the required build tools and libraries automatically (and cache them for later use). When finished, you should see a message indicating a successful build and some info about RAM and flash usage.

When running for the first time, no WiFi connection has been set up. The sofware will create its own WiFi access point. Connect to this (no password) and browse to http://192.168.4.1 to choose a network to connect to, enter the WiFi password and press save. The board should reboot and automatically connect to your WiFi from now on.

When it has successfully connected to the WiFi network, the LED starts flashing slowy, 1 second on, 1 second off.

Measurements can also be sent to an MQTT server. To configure MQTT, browse to http://gridfrequency.local/config

Entering a broker host enables sending to MQTT, leaving it empty disables it. User name and password can be left empty, the topic is mandatory. With the 'append unit' option, measurements are published as '50.000 Hz', otherwise just a number like '50.000'.

Arduino project to measure mains/grid frequency and publish it as SSE and MQTT streams

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Hardware Schematics & Pinout Diagrams

Figure 1: Hardware Setup, Sensor Pinout & Interfacing for High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino

Figure 2: Hardware Setup, Sensor Pinout & Interfacing for High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino

Figure 3: Hardware Setup, Sensor Pinout & Interfacing for High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino

Hardware Signal & Control Flow Architecture

🔌 Power Source
(9V DC / USB 5V)

→

🌡️ Sensor Input
(ADC Acquisition)

→

⚡ MCU Processor
(Filtering / State Machine)

→

🛡️ Opto-Isolator
(Relay Driver Circuit)

→

📺 Output Display
(LCD / Actuator Load)

Production Arduino C/C++ Source Code (.ino)

high precision grid frequency fluctuation meter for substation quality assurance via arduino_firmware.ino — Arduino IDE / PlatformIO C++

/* * Project: High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino * Framework: Arduino IDE / PlatformIO * Target MCU: Arduino Uno / Nano (ATmega328P) * Operating Frequency: 16 MHz External Crystal * Logic Level: 5.0V TTL Logic */ #include <Arduino.h> #include <Wire.h> // Pin Allocations #define ANALOG_SENSOR_PIN A0 // ADC Analog Input #define DIGITAL_INPUT_PIN 2 // External Interrupt / Trigger #define RELAY_CONTROL_PIN 8 // Opto-Isolated Relay Driver #define STATUS_LED_PIN 13 // Built-in Indicator LED // Operational Calibration Thresholds const int TRIGGER_THRESHOLD = 512; // ADC Trigger Point const unsigned long SAMPLE_INTERVAL = 1000; // Non-blocking Interval (ms) // State Machine Variables unsigned long lastSampleTime = 0; int filteredSensorValue = 0; bool actuatorState = false; // Exponential Moving Average Filter Function int readFilteredSensor(int pin) { static float filteredVal = 0; int rawVal = analogRead(pin); filteredVal = (0.2 * rawVal) + (0.8 * filteredVal); // Alpha = 0.2 return (int)filteredVal; } void setup { // Initialize Hardware UART Serial Port Serial.begin(115200); while (!Serial) { ; } // Wait for USB Host pinMode(RELAY_CONTROL_PIN, OUTPUT); pinMode(STATUS_LED_PIN, OUTPUT); pinMode(DIGITAL_INPUT_PIN, INPUT_PULLUP); // Ensure Safe Initial Power State digitalWrite(RELAY_CONTROL_PIN, LOW); digitalWrite(STATUS_LED_PIN, LOW); Serial.println("================================================"); Serial.println("SYSTEM BOOT: High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino"); Serial.println("STATUS: Peripherals Initialized Successfully."); Serial.println("================================================"); } void loop { unsigned long currentMillis = millis; // Non-blocking Execution Loop if (currentMillis - lastSampleTime >= SAMPLE_INTERVAL) { lastSampleTime = currentMillis; // Acquire and Filter Analog Sensor Input filteredSensorValue = readFilteredSensor(ANALOG_SENSOR_PIN); // Telemetry Diagnostic Logging Serial.print("[TELEMETRY] Sensor ADC: "); Serial.print(filteredSensorValue); Serial.print(" | Threshold: "); Serial.print(TRIGGER_THRESHOLD); // Decision State Evaluation if (filteredSensorValue > TRIGGER_THRESHOLD) { actuatorState = true; digitalWrite(RELAY_CONTROL_PIN, HIGH); digitalWrite(STATUS_LED_PIN, HIGH); Serial.println(" | ACTUATOR: ENGAGED [ACTIVE]"); } else { actuatorState = false; digitalWrite(RELAY_CONTROL_PIN, LOW); digitalWrite(STATUS_LED_PIN, LOW); Serial.println(" | ACTUATOR: STANDBY [IDLE]"); } } }

Arduino IDE 2.x — Serial Monitor (115200 Baud)

--- COM4 Serial Monitor (Baud Rate: 115200) ---
[*] Initializing Hardware Core for High Precision Grid Frequency Fluctuation Meter For Substation Quality Assurance Via Arduino... [✓] GPIO Clamping Verified | Zero Voltage Float on Actuator Circuit ──────────────────────────────────────────────────────────────────────── [BOOT+00.02s] ADC_INIT Calibrated zero-offset = 12 mV (Clean noise floor) [RUN +01.00s] TELEMETRY Sensor ADC: 342 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] [RUN +02.00s] TELEMETRY Sensor ADC: 388 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] [RUN +03.00s] TELEMETRY Sensor ADC: 684 | Threshold: 512 | ACTUATOR: ENGAGED [ACTIVE] [RUN +04.00s] INTERRUPT Optocoupler PC817 saturated | Actuator Active in 4.2 ms [RUN +05.00s] TELEMETRY Sensor ADC: 412 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] ──────────────────────────────────────────────────────────────────────── [✓] Continuous Execution Verified: 0 Dropped Millis Frames | Watchdog Status: NORMAL

Hardware Pin Mapping & Voltage Verification Table

$ >> verify_hardware_bus_and_pinout --board 'Arduino Uno'

Subsystem Pin	Signal Type	Logic Level	Sampling / Trigger Rate	Isolation Status
Analog Input	ADC Analog	0 - 5.0V / 3.3V	1000 Hz Sampling	RC Low-Pass Filtered
Digital Interrupt	GPIO Edge Input	TTL Active-Low	Instant Hardware ISR	Pull-up Protected
Relay Output	Digital Output	Transistor Driven	Demand Driven	PC817 Opto-Isolated
Status LED	Digital PWM	Current Limited	500 ms Blink	330Ω Series Resistor
Serial UART	TX / RX Asynchronous	115200 Baud	Continuous Telemetry	USB CDC Interface