Single-Phase Digital Energy Meter with LCD Cost Display

Every electricity bill rests on one measurement: energy, the time-integral of power. Utility meters do this with dedicated metrology chips, but the underlying principle — sample v(t) and i(t), multiply, accumulate — is entirely implementable on a microcontroller and makes an excellent teaching build. It forces engagement with the real subtleties: sampling both waveforms simultaneously, why apparent power differs from real power on reactive loads, how calibration constants map ADC counts to volts and amps, and why a meter must remember its accumulated reading through power cuts. This project builds that meter for a single-phase demo circuit: isolated voltage and current sensing, an Arduino integrating real power into kWh, a tariff-based cost display, and a calibration procedure the student performs with a known resistive load — the honest way to claim accuracy.

1. Isolated voltage sensing (transformer or isolated divider) and a current transformer/Hall sensor feed scaled replicas of the mains waveforms to the Arduino's ADC.
2. The firmware samples both channels in quick succession many times per mains cycle, capturing the waveform shapes.
3. Each sample pair is multiplied to get instantaneous power; the products are averaged over whole cycles to get real power in watts.
4. Real power is integrated over time into watt-hours and accumulated into the kWh register, which is checkpointed to EEPROM.
5. The LCD shows live V, I, W, estimated PF, accumulated kWh and the cost computed from the configured tariff.
6. During setup, the student runs the calibration procedure with a known load, adjusting the voltage and current constants until the meter reads correctly.
7. A deliberate long-press resets the register; ordinary button presses only change the display page.

Tech stack:

• Arduino Uno/Nano (ATmega328P)
• Isolated voltage sensing stage
• Current transformer or Hall-effect current sensor
• 16x2 character LCD
• EEPROM (on-chip) for energy backup
• Arduino IDE (C/C++ firmware)
• Single-phase demo load bank (resistive + reactive loads for PF demo)

• [True power integration] Voltage and current are sampled together and multiplied sample-by-sample, so the meter registers real power (watts) — correctly lower than V×I on reactive loads — not just apparent power.
• [kWh accumulation with EEPROM backup] Accumulated energy is written to EEPROM periodically and on power-fail detection, so the reading survives outages like a real meter.
• [Tariff-based cost display] A configurable per-unit tariff converts accumulated kWh into a running cost figure on the LCD — the part of metering students actually care about.
• [Buyer-run calibration procedure] Calibration constants are set by the student against a known resistive load (e.g. a rated lamp) following the documented procedure; accuracy is earned, not claimed.
• [Live electrical parameters] The LCD cycles through voltage, current, real power, power factor estimate and accumulated energy, not just the final kWh number.
• [Tamper-evident reset] The energy register resets only through a deliberate long-press sequence, demonstrating why real meters protect their registers.
• [Serial data output] Readings are also streamed over serial for logging and plotting on a PC during the demo.

• Working digital energy meter prototype (Arduino, isolated V/I sensing, LCD, demo load bank)
• Complete firmware source code (sampling, power integration, EEPROM backup, tariff math, LCD/serial)
• Circuit and wiring documentation with sensor selection notes
• Component list with ratings
• Calibration procedure (buyer-run: calibrate against a known load, verify with reactive load)
• Project report PDF (energy metering theory, sampling, calibration, methodology, test procedure)
• PPT presentation for final review
• Viva Q&A preparation document (real vs apparent power, sampling, calibration, why EEPROM backup)
• Setup and demonstration guide

• This is an academic demonstration meter, not a utility-billing instrument; it must not be used for actual billing or installed on building wiring.
• Accuracy is a design target achieved through the buyer's own calibration — the meter ships uncalibrated and final accuracy depends on the sensors and the care taken in calibration.
• Single-phase only; three-phase metering needs three sensing channels, noted as an extension.
• The Arduino ADC resolution and sampling rate limit performance on heavily distorted waveforms; this is documented as a teaching limitation.
• Tariff is a single flat rate in the base build; slab/tiered billing is a possible firmware extension.