PeterThePowerMeter

⚡ Peter The Power Meter

with ESP8266 and ADS1115

⚠️ Disclaimer

[!CAUTION]

⚠️ IMPORTANT SAFETY WARNING & DISCLAIMER

THIS PROJECT INVOLVES WORKING WITH HIGH VOLTAGE (230VAC). HIGH VOLTAGE CAN CAUSE SEVERE INJURY, ELECTROCUTION, OR DEATH. FIRE HAZARD IS ALSO PRESENT.

This project is provided "as is", for educational and hobbyist purposes only. By using any part of this project (including hardware designs, PCB layouts, and software), you acknowledge and agree to the following:

• Assumption of Risk: You are solely responsible for your own safety and for any damage caused by the assembly, testing, or use of this device.
• No Liability: The author(s) shall not be held liable for any direct or indirect damages, including but not limited to: hardware failure, data loss, property damage (fire, short circuits), personal injury, or death, resulting from the use or misuse of this project.
• Assembly & Modification: Any errors in assembly, soldering (e.g., solder bridges), component selection, firmware modification or others actions are the sole responsibility of the user.
• No Warranty: There is no guarantee regarding the accuracy of measurements, the stability of the software, or the safety of the hardware design for long-term use.
• Local Standards: It is the user's responsibility to ensure that the device complies with local electrical codes and safety regulations.

IF YOU ARE NOT EXPERIENCED IN WORKING WITH MAINS VOLTAGE, DO NOT ATTEMPT TO BUILD THIS PROJECT.

📜 Revision History

• 00: First release (30/05/2026)
• 01: Hardware optimizations and professional safety compliance updates (17/06/2026)
  • Complete 2.5mm High-Voltage Isolation: Optimized the High Voltage (HV) layout to strictly enforce a minimum 2.5mm track-to-track clearance across the entire mains section. This includes adding physical PCB isolation slots (milling) between R28, R29, F1, and J3 (pin 2), and shifting transformer TR1 along with adjacent resistors slightly upward to eliminate any tight spacings.
  • Industrial-Grade Reinforced Insulation: Preserved the robust 8.0mm isolation barrier natively designed between the HV and Low Voltage (LV) domains. By combining this wide clearance with the new track-to-track optimizations, the board fully satisfies the strict Reinforced Insulation requirements of the IEC/EN 62368-1 standard (aligning with household and industrial appliance safety regulations like IEC 60335-1 / IEC 60730-1), drastically setting this architecture apart from typical, uncertified DIY designs.
  • Power Rail & Logic Level Optimization: Removed 1 pin from connector J11 to eliminate the +5VDC routing to the lateral pcb, successfully migrating the CH340C USB-to-Serial subsystem entirely to a +3.3VDC power rail.
  • Component Reconfiguration: Rewired pin 4 (V3) of the CH340C directly to the +3.3VDC rail (mandatory for stable 3.3V operation) while retaining C9 in the layout to act as an active power supply decoupling filter instead of a standard bypass to GND.

💡 Design Rationale & Project Overview

1.1 System Architecture

This project is a Digital Power Meter designed for real-time energy monitoring with acoustic alarm when a threshold is exceeded. The system is engineered to fit within a standard 1-module DIN rail enclosure (roughly the size of a standard miniature circuit breaker), making it ideal for integration into domestic electrical panels.

Note: At the moment, the 3D design/CAD file for the DIN enclosure is not available. Contributions regarding the design of a suitable enclosure are highly welcome and would be a valuable addition to this project.

The system architecture is based on the ESP8266 (ESP-12F) microcontroller, leveraging its Wi-Fi capabilities for IoT integration and an ADS1115 to read voltage and current. For system health, an onboard TFPT1206L1002DV temperature sensor is included to monitor the internal thermal conditions of the enclosure.

For local interaction, the device features a 0.96" color LCD display that provides real-time data visualization and configuration menus. Users can navigate through multiple data pages and perform basic setup tasks using a multi-function physical button. Additionally, the system hosts a built-in Web Server, allowing for advanced remote configuration, firmware updates (OTA), and detailed system management via an intuitive Web UI.

The measurement stage utilizes two primary sensors:

• Voltage Sensing: Handled via a dedicated voltage transformer ZMPT107-1 (TR1) for galvanic isolation and safety.
• Current Sensing: Implemented using the SCT-013 split-core current transformer (clamp meter).

Both sensors provide a 1VAC sinusoidal output. These signals are conditioned via a voltage divider network and sampled by an ADS1115 16-bit ADC, which communicates with the MCU via the I2C protocol.

1.2 Hardware Features & User Interface

To optimize GPIO usage, a PCF8574 I/O expander is employed for digital signal management and future use. The user interface consists of:

• Buttons: A multi-function navigation button (Short press: Page toggle | Long press: Confirm/Action) and a dedicated Pin-hole Hardware Reset button connected directly to Pin 1 (RST) of the ESP8266.
• Acoustic Feedback: An active piezoelectric buzzer triggers an audible alarm when a software-defined power threshold is exceeded.
• Thermal Monitoring: An onboard TFPT1206L1002DV temperature sensor (PTC thermistor) is integrated into the circuit. This component allows the system to monitor the internal temperature of the enclosure.
• Display: A 0.96" Color LCD for local monitoring and basic interaction.
• Web Server: A Web User Interface for remote monitoring and full system configuration.

1.3 Power Supply & Protection

The device supports 2 power input options and 1 input 230VAC for Voltage reading:

• Terminal Block (J1): Accepts a +5VDC regulated supply.

[!CAUTION] No reverse polarity protection: This input currently lacks reverse polarity protection; correct orientation is mandatory.

• USB Connector (J2): For secondary power or debugging.

  • Communication & Debugging: This interface utilizes a CH340C USB-to-Serial bridge and a UMH3NFHATN transistor pair to communicate with the ESP8266. This setup enables full debugging, serial communication, and firmware programming (automatic reset/bootloader entry).
  • Safety Feature: The board implements a dual Schottky diode protection circuit on the positive rails of both J1 and J2. This prevents back-feeding, though it is recommended to disconnect J1 when using USB power.
  • Overcurrent Protection: The +5VDC main rail is protected by a MF-NSMF050-2 PTC (Resettable Fuse) rated at 500mA.

• AC Voltage Input (J3): High-voltage input for the ZMPT107-1 transformer.

  • Polarity Recommendation: Although the transformer operates on AC, it is strictly recommended to respect the Phase (L) and Neutral (N) markings.

  

  • Safety Rationale: The protection fuse is located exclusively on the Phase line. Inverting the polarity would mean that, in the event of a fault or a blown fuse, the Neutral line would be disconnected while the entire internal circuit remains energized (live) through the Phase line. This creates a severe electrocution hazard even when the device appears to be non-functional.
  • Safety Design: The circuit features a 250mA T (Slow-blow) fuse placed exclusively on the Phase line. Additionally, the line is equipped with three resistors in series designed to limit the current to 1mA RMS at 230V, providing an essential layer of protection for the sensing stage.

1.4 Operational Limits & Grid Compatibility

This device is specifically designed and calibrated for 230VAC/50Hz Phase-Neutral grids (Standard European Grid).

• Voltage Specificity: The internal components, including the protection resistors and the ZMPT107-1 transformer ratio, are optimized for 230V. Use with different mains voltages (e.g., 110-120V) may result in inaccurate readings or insufficient signal-to-noise ratio.
• Frequency Specificity: The system is tuned for 50Hz operation. While the magnetic components (TR1 and CT) can physically handle 60Hz, the firmware's sampling window and RMS calculation algorithms are optimized for a 20ms period.
• Warning: Operation on different grid standards, high-voltage industrial lines, or Phase-to-Phase configurations (without a neutral line) may exceed the safety ratings of the components and the fuse, leading to hardware failure or fire hazard.

🌐 2.0 Connectivity & Software Integration

The firmware architecture features a built-in Web Server for real-time monitoring, local configuration, and connections management (Wi-Fi and MQTT). The device natively supports the MQTT protocol for a smart home integration with platforms such as Home Assistant.

2.0.1 LCD User Interface (Vertical Orientation)

Navigation is handled via the multi-function button (Short press: Page toggle | Long press: Confirm/Action).

• Page 1: Real-time Monitor
  • Power: Current power consumption displayed in kW.
  • Temperature: PCB temperature in °C.
  • Graph: A rolling history graph showing power trends (approx. 1-minute window).
  • Status Badges: Dynamic icons for Wi-Fi connection status and MQTT connection status.
• Page 2: Power Threshold Configuration
  • Displays the active alarm threshold (Watts).
  • Allows cyclic adjustment of the new threshold (100W increments) via long-press.
• Page 3: Voltage Monitoring
  • Displays the real-time mains voltage (V).
• Page 4: Acoustic Alarm Settings
  • Displays and cycles through buzzer modes: Continuous, Slow Intermittent, or Fast Intermittent.
• Page 5: Save Settings
  • Summarizes settings. Action: A long-press commits settings to non-volatile memory.
• Page 6: System Information
  • Displays network details: Hostname, SSID, IP Address, and Firmware Version.
• Page 7: System Tools
  • AP Mode, Reboot device, and Reset (Factory Reset). Requires a long-press with a visual timer-bar.

2.0.2 Web Interface & Configuration

The device features a responsive Web UI. Users can connect via browser to the device's IP (visible on LCD page 6).

Home Page (Real-Time Dashboard)

• Connectivity Status: Dynamic badges for AP Mode, Wi-Fi, and MQTT.
• Live Telemetry: Power (W), Voltage (V), Current (A).
• System Uptime: Tracks operational time in "Days hh:mm:ss" format.
• Data Refresh: Auto-refresh every 10 seconds or manual button.

Configuration Page

• General Settings: Hostname, Manufacturer, Language (IT/EN), Alarm Threshold, Buzzer Mode.
• Wi-Fi Setup: Credentials and IP Assignment (DHCP or Static IP).
• MQTT Setup (Optional): Broker IP, Port, and Authentication.
• Buttons: Save & Reboot, Reboot, Firmware Update (OTA), Home.

🛠️ Manufacturing & Assembly Notes

3.0 Hardware Configuration

ADS1115 I2C Address Selection: Hardware-defined through two "0-Ohm bridge" resistors: R16 and R17. Only one of these resistors must be populated at a time:

• R16: Connects the ADDR pin to +3.3V, ADS1115 Address 0x49
• R17: Connects the ADDR pin to GND, ADS1115 Address 0x48 (Default).

Safety Design: To prevent assembly errors, the PCB layout utilizes a shared common pad for both R16 and R17. This physical constraint makes it nearly impossible to populate both resistors simultaneously, effectively protecting the +3.3V rail from a direct short circuit to Ground. However, be careful when assembling.

Assembly Layout: TOP Layer

Assembly Layout: BOTTOM Layer

Dimensions

💻 4.0 Firmware

Peter The Power Meter has an embedded firmware designed for real-time single-phase energy monitoring. The system samples AC voltage and current waveforms, calculates Root Mean Square (RMS) values and active power consumption, provides a multi-page visual interface on a TFT display, and integrates with home automation systems via the MQTT protocol.

Technical Specifications

• Language: C++ (Standard C++11/14).
• Framework: Arduino Core for ESP8266.
• Development Environment: PlatformIO.
• Core Hardware: Espressif ESP8266 (e.g., Wemos D1 Mini).
• Data Acquisition: External ADS1115 16-bit ADC connected via I2C for high-precision differential sampling.
• Sensor Support: Current Transformers (SCT-013), Voltage Transformers (ZMPT107-1), and PTC temperature sensors (TFPT1206).

Key Features

• High-Speed Sampling & RMS Calculation: Performs rapid sampling of sinusoidal signals to calculate precise Voltage RMS, Current RMS, and Active Power (W) over a sliding 1-second window.
• Display Management: Features a multi-page User Interface on an ST7735 (0.96" TFT) display; includes real-time power trend graphs, connectivity status badges, and system information pages.
• IoT & Home Automation:
  • MQTT Telemetry: Transmits energy data using a time-weighted average calculated over the publishing interval (default 20s).
  • Home Assistant Integration: Fully supports Auto-Discovery, automatically creating sensors and configuration entities (Select/Number) within Home Assistant.
• Embedded Web Server: A built-in web portal protected by HTTP Basic Authentication allows users to configure WiFi credentials, MQTT settings, alarm thresholds, and perform fine sensor calibration (offset and scale).
• Alarm System: Manages a buzzer via a PCF8574 I/O expander with programmable modes (Continuous, Slow Pulse, Fast Pulse) triggered when power exceeds a user-defined threshold.
• Reliability & Maintenance:
  • Resilient Connectivity: Implements an exponential backoff strategy for WiFi and MQTT reconnection.
  • OTA Updates: Supports Over-The-Air firmware updates through the web interface.
  • Localization: Built-in multi-language support (English and Italian) using PROGMEM to optimize RAM usage.

4.0.1 Sensor Calibration & Physics Guide (include/config.h)

The following constants define how the raw electrical signals from the sensors are translated into human-readable values (Amps, Volts, Watts).

Current Conversion (FACTOR_A_V)

• Description: This is the scaling factor for the Current Transformer (CT). It converts the voltage measured by the ADC into RMS Amperes.
• Formula: I_RMS = V_ADC * FACTOR_A_V.
• Configuration: The FACTOR_A_V of 25.0f is set based on the characteristics of the SCT-013 current transformer.
• When to change:
  1. You replace the SCT-013 with a model that has a different Current/Voltage ratio (e.g., 30A/1V or 100A/50mA).
  2. You add or change an external burden resistor in parallel with the CT output.

Voltage Conversion (FACTOR_V_V)

• Description: This factor scales the low-voltage signal from the ZMPT107-1 transformer back to the actual grid voltage.
• Formula: V_Grid = V_ADC * FACTOR_V_V.
• Configuration: The FACTOR_V_V of 246.0f is derived directly from the ratio of the primary resistance (246KΩ) to the burden resistance (1KΩ).
• When to change: If you modify the scaling "divider" (e.g., changing series resistors on the Primary side or the burden resistor on the Secondary side).

ADC Precision & Sampling Rate

• ADC Precision: ADS_GAIN (GAIN_TWO) sets the full-scale range to ±2.048V, with an ADS_MULTIPLIER of 0.0000625.
• Sampling Rate: 860 Samples Per Second is the maximum stable rate for the ADS1115 and provides high fidelity for power calculations.

Noise, Safety, and Temperature

• CURRENT_NOISE_FLOOR (0.002f): A software filter that forces the current to 0.0A if the measured voltage is below 2mV.
• VOLTAGE_MIN_THRESHOLD (50.0f): If the measured voltage is below 50V, the system assumes the sensor is faulty and falls back to 230V.
• Temperature Monitoring: The firmware averages 10 readings (PTC_AVG_SAMPLES) to stabilize the PTC sensor data; if the temperature exceeds TEMP_WARNING_THRESHOLD (45.0°C), the display text turns RED.

4.0.2 Per-device calibration limits (include/config.h)

These constants define the acceptable range and default values for the calibration parameters stored in EEPROM.

• Scale Factors: CAL_SCALE_DEFAULT is 1.0f (no correction), with a range between 0.1f and 10.0f.
• Voltage Offset Limits: -500.0f to 500.0f Volts.
• Current Offset Limits: -100.0f to 100.0f Amperes.
• Temperature Offset Limits: -50.0f to 50.0f degrees Celsius.

4.0.3 PTC Calibration & Hardware (include/config.h)

The device monitors internal temperature using the TFPT1206 series PTC sensor.

• PTC_V_SOURCE: 3.3f (Standard logic voltage).
• PTC_R_PULLUP: 33,000 Ω (Fixed resistor R7).
• ADC Compensation: Constants PTC_R_DIVIDER_TOTAL and PTC_R_DIVIDER_LOAD compensate for the voltage divider on the ESP8266 ADC input stage.
• Sensor Characteristics: PTC_NOMINAL_RES (10,000 Ω at 25°C) and PTC_COEFF (0.00411) define the resistance-to-temperature curve.

🤝 Contributing

Contributions, issues, and feature requests are welcome! Feel free to open an issue or submit a pull request.

🔜 Coming Soon

I am currently in the process of refining and cleaning up the firmware comments to ensure the code is as clear and readable as possible, even though the project is fully functional. I am also polishing the documentation and preparing additional guides that I'll upload to the repository soon. Currently seeking help with:

• Enclosure Design: I'm looking for contributors to design a 3D-printable enclosure compatible with a standard 1-module DIN rail format. I think I'll be able to upload at least the STL file soon, but not the project.

📝 License

This project is licensed under the MIT License. See the LICENSE file for details.

👤 Author

CtrlAltJon