Smart Switch — ESP-Based Wi-Fi Smart Home Controller

Overview

Smart Switch is an embedded IoT home automation system designed and built by Javed Hussain. Unlike conventional smart-home products that become unresponsive when the internet drops or cloud servers experience downtime, Smart Switch is engineered with an uncompromising offline-first philosophy: physical household wall switches retain absolute reliability and control, while local Wi-Fi and web capabilities serve as an enhancement rather than a point of failure.

Built around the ESP32 microcontroller and a 4-channel active-LOW relay module, the system interfaces directly with traditional residential toggle switchboards, providing instant mechanical switching alongside responsive local network controls.

Project Metadata

• Category: Embedded Systems / IoT / Hardware Prototyping
• Status: Completed Working Prototype (MVP v1 – v4)
• Controller: Espressif ESP32 Dev Module (ESP32-WROOM-32)
• Firmware Framework: C++ / PlatformIO (Arduino Core for ESP32)
• Author / Developer: Javed Hussain (@iamjaved026)
• Primary Focus: Offline-First Switching, Boot-Time State Synchronization, Hardware Isolation, Local Captive Portal

Why I Built It

Most commercial smart switches available on the market suffer from fundamental architectural flaws:

1. Cloud Dependency: If the home Wi-Fi router restarts or the cloud provider experiences an outage, lights and appliances cannot be toggled.
2. Ignoring Physical Wall Switches: Many smart modules force users to use an app or voice assistant, confusing family members who naturally reach for the wall switch.
3. Power-Cut Glitching: When electricity returns after a blackout, poorly designed microcontrollers often cycle relays randomly, turning every connected light ON in the middle of the night.

Living in Teghra, Bihar, where intermittent power interruptions and network fluctuations occur, I set out to build a smart switch that feels as instant, tactile, and trustworthy as a traditional mechanical switch, while adding modern wireless convenience.

Hardware Architecture & Physical Test Rig

The prototype was constructed and validated using a dedicated desktop test bench that mimics a real Indian household switchboard:

• Microcontroller: ESP32 Dev Module with 30-pin layout, dual-core Xtensa 32-bit LX6 processor.
• Relay Board: 4-Channel Active-LOW Relay Module utilizing Songle SRD-05VDC-SL-C electromechanical relays (rated up to 250V AC / 10A), optocoupler isolation, and red channel indicator LEDs.
• Physical Switch Interface: 4-gang Indian modular wall switchboard with traditional mechanical toggle switches, connected to ESP32 inputs with low-voltage signal wiring and common GND.
• Status Indication: Low-voltage status LED on GPIO 15 with current-limiting resistor.
• Power Provisioning: Dual-rail testing with 5V USB for logic development and an external 2x 18650 Li-ion battery pack for decoupled testing.

Signal & Control Flow Architecture

  [ Physical Wall Switches ] ────────┐
  (4x Mechanical Toggles)            │
                                     ▼
                        [ ESP32 Microcontroller ]
                        ┌───────────────────────────────┐
  [ Local Smartphone / Web ] ──►│ Debounce Engine (millis())    │
  (192.168.4.1/dash Portal)     │ Boot-Time State Sync Logic    │
                                │ NVS State Memory Storage      │
                                └──────────────┬────────────────┘
                                               │ (Active-LOW Logic)
                                               ▼
                                  [ 4-Channel Relay Board ]
                                  (Optocoupler Galvanic Isolation)
                                               │
                                               ▼
                                   [ 230V AC Household Loads ]
                                   (Fans, Lights, Appliances)

GPIO Pin Assignment & Safety Engineering

Selecting GPIO pins on the ESP32 requires careful attention to hardware constraints. During development, critical design rules were established to prevent ghost signals and boot failures:

Critical Hardware Learning: GPIO 34–39 on the ESP32 are input-only pins and lack internal pull-up/pull-down resistors. Attempting to use them for switch inputs without external pull-up resistors causes floating, noisy inputs. They were intentionally excluded from switch duties in favor of GPIOs 32, 33, 18, and 19.

Key Capabilities & Firmware Features

1. Deterministic Boot-Time State Synchronization

When power is restored after an electrical cut, the ESP32 initializes all relay pins to HIGH (the safe, non-energized state for active-LOW relays) to eliminate boot-time clicking. Within milliseconds, the firmware reads the actual physical position of each wall toggle switch and immediately commands the relays to match:

• Switch physically ON ➔ Relay energizes ON.
• Switch physically OFF ➔ Relay remains OFF.
• No unexpected light toggles in the middle of the night.

2. Non-Blocking Debouncing Engine

Mechanical wall switches produce electrical contact bounce (microsecond noise spikes) when toggled. The firmware implements a non-blocking debouncing algorithm using millis():

• Detects raw pin state transitions instantly.
• Waits for signal stability across a configurable debounce threshold before committing state updates.
• Eliminates ghost toggling caused by nearby electromagnetic interference (EMI) or arcing.

3. Onboard Captive Portal & Web Dashboard

The ESP32 runs an embedded asynchronous HTTP server (ESPAsyncWebServer) that serves a complete HTML5/CSS3 control dashboard directly from flash memory:

• AP Mode Provisioning: Broadcasts a local Wi-Fi hotspot (SmartSwitch-AP) allowing any smartphone to connect directly at 192.168.4.1/dash without needing internet access.
• Interactive Toggles: Individual switches for Relays 1 through 4, accompanied by master "All ON" and "All OFF" actions.
• Network Scanner: The /api/wifi-scan endpoint scans local 2.4 GHz networks, reporting SSIDs, signal strengths (RSSI), and encryption types to facilitate wireless configuration.
• Local Network mDNS: Once connected to the home router, the device resolves automatically to http://smartswitch.local.

4. Read-Back Verification & Serial Telemetry

Every relay command is verified in hardware. After executing a digitalWrite, the firmware immediately reads the pin's state back via digitalRead and outputs formatted telemetry over the serial interface at 115200 baud, enabling transparent debugging of electrical behavior.

Development Evolution: From Prototype to Product Thinking

The project progressed across multiple disciplined engineering iterations:

• MVP v1 (19 Jan 2026): Proved the offline-first foundation. Implemented 4 physical wall switches, 4-channel active-LOW relay driver, boot-time state sync, and strict serial logging.
• MVP v2 (20 Jan 2026): Added Non-Volatile Storage (NVS) memory support via the ESP32 Preferences library to persist relay states and user preferences across reboots.
• MVP v3 (24 Jan 2026): Introduced the onboard captive portal, local network web dashboard (192.168.4.1/dash), and asynchronous REST API endpoints for wireless phone control.
• MVP v4 (Feb–Mar 2026): Engineered multi-network management, device authentication tokens, watchdog timer recovery, and an experimental Python Firestore cloud bridge simulator for remote synchronization.
• Firmware Security Auditing: Extracted raw firmware binaries (bootloader.bin, firmware.bin, firmware.elf) and conducted reverse engineering disassembly testing using Ghidra to understand IoT attack surfaces and memory protection.

Implemented vs. Designed vs. Planned

Mains Safety & High-Voltage Isolation

Switching real 230V AC household electrical loads carries genuine safety considerations:

• Galvanic Isolation: The low-voltage ESP32 circuit (3.3V logic) is physically isolated from the high-voltage mains AC lines through the relay module's onboard optocouplers.
• Enclosure & Clearance: In practical deployment, mains-carrying conductors must reside inside flame-retardant enclosures with physical separation and creepage clearance slots separating high-voltage traces from low-voltage logic.
• Overcurrent Protection: The hardware architecture mandates an upstream fast-blow fuse and Metal Oxide Varistor (MOV) for transient voltage surge suppression.

Explore the Build Story & Architecture

• Developer Build Story: Building My ESP32 Smart Switch: From Prototype to Custom Hardware
• About the Builder: About Javed Hussain
• Technical Skills Matrix: Explore Embedded & IoT Skills