GridSeis - DIY Grid Frequency Monitor

Build your own real-time power grid frequency monitor using an ESP32 and a servo motor. Watch the needle move as the UK grid fluctuates around 50Hz.

No external sensors required - the ESP32 picks up the 50Hz electromagnetic field from nearby mains wiring using just a short wire antenna (or even nothing at all).

What You'll MAke

A collection of wires and a microcontroller with a servo connected that (when paired with a box to put it in and a dial) will show:

• Centre position = 50.00 Hz (nominal)
• Left = Demand > Supply
• Right = Demand < Supply

Parts List

Part	Approx. Cost	Notes
ESP32 DevKit	£5-10	Any ESP32 board works (ESP32, ESP32-S2, ESP32-S3)
MG996R Servo	£5-8	Or any standard hobby servo
Jumper wires	£2	3 wires for servo, 1 optional for antenna
USB cable	-	For power and programming

Total: ~£12-20

Wiring

ESP32                MG996R Servo
─────                ────────────
GPIO 4  ──────────►  Orange (Signal)
5V      ──────────►  Red (Power)
GND     ──────────►  Brown (Ground)

GPIO 34: Leave floating or attach 10-30cm wire as antenna

Wiring Diagram

                    ┌─────────────────┐
                    │     ESP32       │
                    │                 │
    ┌───────────────┤ GPIO 4          │
    │               │                 │
    │   ┌───────────┤ 5V              │
    │   │           │                 │
    │   │   ┌───────┤ GND             │
    │   │   │       │                 │
    │   │   │       │ GPIO 34 ────────┼──── Optional: 10-30cm wire antenna (a dupont wire works fine!)
    │   │   │       │                 │
    │   │   │       └─────────────────┘
    │   │   │
    │   │   │       ┌─────────────────┐
    │   │   │       │  MG996R Servo   │
    │   │   │       │                 │
    └───┼───┼───────┤ Orange (Signal) │
        │   │       │                 │
        └───┼───────┤ Red (Power)     │
            │       │                 │
            └───────┤ Brown (Ground)  │
                    │                 │
                    └─────────────────┘

Wiring Tips

• Use a GND pin away from 5V - the GND pin closest to 5V can cause issues with the servo. Use one on the other side of the board
• Servo jittering? The servo draws a lot of current. If it jitters or resets the ESP32, power the servo from a separate 5V supply (share GND with ESP32)
• No signal? Try moving closer to a wall socket or power strip - the 50Hz field is stronger near mains wiring

Software Setup

1. Install VS Code + PlatformIO

PlatformIO handles all the toolchain setup automatically - no need to install anything else.

1. Install VS Code: Download from https://code.visualstudio.com/

2. Install PlatformIO Extension:

   • Open VS Code
   • Go to Extensions (Ctrl+Shift+X / Cmd+Shift+X on Mac)
   • Search "PlatformIO IDE"
   • Click Install
   • Wait for it to finish (it downloads compilers etc.)

2. Get the Code

git clone https://github.com/JamesTwallin/GridSeisMonitor.git

Or download as ZIP from GitHub and extract.

3. Open in VS Code

• File → Open Folder → select the GridSeisMonitor folder
• VS Code will ask if you trust the folder - click Yes
• Wait for PlatformIO to initialise (first time takes a few minutes)

4. Build and Upload

1. Connect your ESP32 via USB
2. Click the → (right arrow) icon in the blue status bar at the bottom
   • Or use the keyboard shortcut: Ctrl+Alt+U
3. PlatformIO will auto-detect your board and upload

5. View Output

You need a serial monitor to see the data. Two options:

Option A: PlatformIO's built-in monitor

• Click the plug icon in the blue status bar at the bottom
• Or press Ctrl+Alt+S

Option B: Serial Monitor extension (recommended)

1. Install "Serial Monitor" extension by Microsoft from the VS Code marketplace
2. Click the serial monitor icon in the left sidebar (looks like a plug)
3. Select your COM port from the dropdown
4. Set baud rate to 115200
5. Click "Start Monitoring"

You should see frequency readings like: {"t":12345,"freq":50.0123,"signal":0.5}

How It Works

1. Signal Pickup: The ESP32's ADC samples electromagnetic interference from nearby mains wiring at 1000 Hz. Even a floating GPIO pin picks up the 50Hz hum.

2. IQ Demodulation: The firmware correlates the signal with reference 50Hz sine and cosine waves to extract the phase.

3. Frequency Calculation: By measuring how the phase drifts between 1-second windows, we calculate the actual grid frequency to ~0.001 Hz precision.

4. Servo Display: The frequency is mapped to a servo angle, giving you a physical dial that responds in real-time.

Data Logging (Optional)

The ESP32 outputs JSON data over serial that you can log and plot.

How to Run The Python Code

I've created a minimal environment with miniconda. I make a conda env:

conda create -n grid_seis python=3.12

and use pip to manage the packages:

pip install -r requirements.txt

Capture Data

python capture.py

That's it - it auto-detects your ESP32 and logs to a timestamped file (grid_log_YYYYMMDD_HHMMSS.jsonl). Press Ctrl+C to stop.

Plot Data

python plotter.py

This creates a graph comparing your ESP32 readings against official grid data (if available).

Compare with Official Grid Data

UK grid frequency data is available at: https://www.nationalgrideso.com/data-portal/system-frequency-data

More immediate frequency data: https://bmrs.elexon.co.uk/rolling-system-frequency

Download the "Rolling System Frequency" CSV/JSON and place it in the project folder.

Serial Output Format

The ESP32 outputs JSON lines at 115200 baud:

{"t":12345,"freq":50.0123,"signal":0.543}

Field	Description
t	Timestamp (ms since boot)
freq	Measured frequency (Hz)
signal	Signal amplitude (0-1, higher = stronger pickup)

USB Drivers

Your ESP32 board has a USB-to-serial chip that needs a driver. If your board isn't detected, this is usually why.

Which chip do I have?

Look at the small chip near the USB port on your board:

• CP2102 or CP2104 (square, says "SILABS") → Need CP210x driver
• CH340 or CH341 (rectangular, says "CH340") → Need CH340 driver
• No chip visible (ESP32-S2/S3 with native USB) → No driver needed

Download Links

Chip	Windows	Mac	Linux
CP210x	Silicon Labs	Silicon Labs	Built-in
CH340	WCH	WCH	Built-in

After Installing

1. Unplug and replug your ESP32
2. Check it appears:
   • Windows: Device Manager → Ports (COM & LPT) → should show "Silicon Labs CP210x" or "USB-SERIAL CH340"
   • Mac: Terminal → ls /dev/tty.usb*
   • Linux: Terminal → ls /dev/ttyUSB* or ls /dev/ttyACM*

Troubleshooting

Servo doesn't move

• Check wiring (especially the signal wire to GPIO 4)
• Ensure servo is getting 5V (some USB ports can't supply enough current)
• Try a powered USB hub or external 5V supply for the servo

Readings are unstable

• Move closer to mains wiring (near a wall socket or power strip)
• Try attaching a 10-30cm wire antenna to GPIO 34
• Ensure good grounding

Frequency seems wrong

• The measurement needs ~10 seconds to stabilise after power-on
• Check you're in a 50Hz country (UK, Europe, etc.)

Can't upload to ESP32

• Check USB drivers are installed (see USB Drivers section above)
• Try a different USB cable (some are charge-only, with no data wires)
• Hold the BOOT button while clicking upload, release after "Connecting..." appears
• Some boards need you to hold BOOT, press EN/RST, then release both

Project Structure

GridSeisMonitor/
├── main/
│   ├── main.c           # Firmware source code
│   └── CMakeLists.txt   # Component build config
├── CMakeLists.txt       # Project build config
├── platformio.ini       # PlatformIO settings
├── capture.py           # Log serial data to file
├── plotter.py           # Plot frequency data
└── requirements.txt     # Python dependencies

Contributing

Pull requests welcome! Some ideas:

• Support for different servo types
• OLED/LCD display option
• WiFi data upload

Acknowledgements

• Grid frequency data from National Grid ESO
• Elexon frequency data Elexon
• Inspired by Bertrik

License

MIT License - do whatever you want with this code.