Smart Power Strip with Per-Outlet Energy Monitoring, Scheduling and Android App (ESP32)

Electricity bills arrive as a single number, so nobody knows which device actually wastes power. A whole-house energy meter shows only the total — the charger left on all night, the old table fan, the room heater — every load hides inside one monthly figure. Single-outlet smart plugs solve one socket at a time, are usually locked to a vendor's cloud, and give no honest per-outlet measurement for the rest of the board. The result is that households cannot answer the basic question of where their units go, and energy-saving advice stays generic. This project builds the missing middle: a 4-outlet smart extension board where every outlet is individually switched and individually measured. Each outlet carries its own PZEM-004T energy sensor on a unique Modbus address, so voltage, current, active power and cumulative energy are read per outlet, not estimated from the total. Daily schedules run on the ESP32 itself with an NTP-synced clock, and a companion Android app gives live readings, toggles and tariff-based cost estimates over local Wi-Fi. Built from standard parts with a documented calibration procedure, it is a complete mains-interfacing IoT build a student can genuinely explain and defend.

1. Each of the 4 Indian 3-pin outlets is wired through its own channel of the 4-channel relay module and its own PZEM-004T sensor, each PZEM set to a unique Modbus slave address.
2. The ESP32 polls the four sensors over UART (Modbus RTU) about once per second, collecting voltage, current, active power, cumulative energy, frequency and power factor per outlet.
3. The firmware checks each reading against the on-device schedule table and the per-outlet overload limit; on overload it opens that outlet's relay, sounds the buzzer and publishes a trip event.
4. Readings and relay states are published over Wi-Fi to the local MQTT broker, and the ESP32 exposes a lightweight HTTP API for direct outlet control.
5. The Android app (Kotlin) connects over the same Wi-Fi network: live per-outlet cards, on/off toggles, a schedule editor, and cost estimates computed from measured kWh and the configured tariff.
6. Schedules, tariff and relay-state policy live in ESP32 flash — the strip executes timers standalone, so the app is the control surface, not a dependency.
7. Before final testing, the student runs the included calibration procedure with a known reference load to verify each channel's readings and documents the result in the report.

Tech stack:

• ESP32 development board (Wi-Fi, Modbus polling, scheduling, MQTT)
• PZEM-004T energy sensor modules × 4 (one per outlet)
• 4-channel relay module (10 A 250 VAC per datasheet)
• Arduino (C++) firmware on ESP32
• MQTT (Mosquitto-class local broker) + HTTP API
• Android app in Kotlin
• NTP time sync for schedules
• HTML/JS energy dashboard (demo + report visuals)

• [Per-outlet energy measurement] Each of the 4 outlets has its own PZEM-004T module on a unique Modbus address, measuring voltage, current, active power, cumulative energy (kWh), frequency and power factor for that outlet alone. Nothing is inferred from the total — this is what separates the build from a whole-house meter or a single smart plug.
• [Per-outlet relay switching] A 4-channel relay module (10 A 250 VAC per datasheet) switches each outlet independently from firmware, schedules or the app. The on/off state is stored in flash and is configurable: restore-last-state or default-all-off after a power cut.
• [On-device scheduling] Daily timers live in ESP32 flash and run on an NTP-synced clock — e.g. Outlet 2 (charger) OFF 23:00–06:00, Outlet 4 (heater) limited to evening hours. Schedules execute with no phone and no internet present.
• [Overload cut-off] The firmware opens an outlet's relay when its current crosses the configurable limit (default 6.5 A per outlet, design target) and sounds the buzzer while the app flags the event. The incoming mains line is fused.
• [Android companion app] A Kotlin app connects over local Wi-Fi: live per-outlet cards with W/A/kWh, on/off toggles, a schedule editor, and monthly cost estimates from measured energy at the configured tariff (default ₹8/unit, configurable).
• [Local MQTT telemetry] Readings and relay states are published to a local Mosquitto-class broker, and the ESP32 also serves a lightweight HTTP API for direct control. Remote/cloud access is an optional configurable extension, not part of the base build.
• [Energy and cost accounting] Cumulative kWh per outlet accumulates in non-volatile storage; the app converts measured energy into a monthly cost estimate so the student can show real savings in the report.
• [Buyer-run calibration procedure] A documented routine compares each channel's readings against a known reference load, so measurement accuracy is verified on the student's own build and can be honestly reported in the viva.

• Assembled 4-outlet smart power strip prototype (ESP32, 4 × PZEM-004T, 4-channel relay board, fused mains inlet, labeled enclosure)
• ESP32 firmware (C++): Modbus polling, scheduling engine, MQTT + HTTP API, overload logic
• Android app source code (Kotlin) with an installable APK
• Wiring diagram and per-outlet sensor address map
• Buyer-run calibration procedure document
• HTML energy dashboard demo (live simulated readings, toggles, schedules, cost estimate)
• Project report PDF (10 sections), PPT presentation, viva Q&A document

• Each outlet is limited to 6 A by the socket rating (1380 W at 230 V design target) — a 2000 W heater exceeds this and must not be connected; keep heavy loads within the limit.
• Measurement accuracy is datasheet-grade (±1% on power/energy), not calibrated lab instrumentation; the included procedure lets the buyer verify each channel on their own build.
• Outlets share a common neutral busbar — per-outlet measurement is on the phase side, which is standard for this class of build.
• Only overload cut-off is implemented per outlet; there is no per-outlet earth-leakage protection, so an ELCB/RCCB in the installation is still required.
• Wi-Fi is 2.4 GHz only with the router's range; there is no cellular or long-range radio in the base build.
• Cloud dashboard and remote-outside-LAN control are not included in the base build — control is over local Wi-Fi (available as a configurable extension).
• Cumulative energy history lives in flash; a factory reset clears the stored totals.