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🔌 Hardware

The first commercial product is a switch+light kit — two ESP32 devices that replace a regular wall switch and ceiling light, paired automatically via kit_tag over BLE.

Positioning​

  • Market: premium / smart-home enthusiasts (priced between Shelly/Sonoff and Lutron Caseta).
  • Install path: electrician-installed, not DIY. End-user just sees a normal switch that also has app/voice control.
  • Closest competitors: Aqara H1, Philips Hue (with comparable positioning, but local-first and open-source).

Kit Composition​

esp32-switch-pir​

  • Mounts in a standard in-wall box, replaces a regular wall switch
  • Latching 220V relay (Omron G5RL-K or Hongfa HFD3) — physically switches mains to the lamp fixture
  • Tactile button (momentary, not toggle) — lit by an LED indicator on the front face
  • PIR sensor (HC-SR501) — motion detection
  • Hardware T-flip-flop between button and relay driver (74HC74 + 74HC123 edge detector) — keeps button → light working even if the ESP32 dies
  • Powered by HLK-PM03 isolated AC/DC module (220V → 5V)

esp32-light​

  • Mounts inside the lamp fixture
  • SELV-only board (no 220V inside) — fed by external 12V brick
  • MP1584EN buck (12V → 5V) + LDO for ESP32 (3.3V)
  • 3× MOSFET (IRLZ44N) for 3-channel CCT LED strip (Warm/Neutral/Cool white)
  • No RGB in this revision (would need different LED strip)

Architectural Principle: Local-First​

The physical toggle of the switch must not depend on the network or the microcontroller.

The path button → light is purely hardware:

button → RC debounce → 74HC74 T-flip-flop → 74HC123 edge detector
       → dual MOSFET driver → latching relay coil → 220V to lamp

ESP32 sits in parallel to this path:

  • Reads the button GPIO for long-press detection and MQTT events
  • Reads the flip-flop's Q output to know current state
  • Can override state via PRE/CLR lines (for MQTT commands and PIR automations)

Failure Modes​

FaultEffect on basic on/off
Wi-Fi router down✅ Switch works locally
Station (RPi + MQTT) down✅ Switch works locally
ESP32 in light dies✅ Relay still feeds 220V → lamp on at default brightness
ESP32 in switch dies✅ Button works (flip-flop is hardware); only MQTT features lost
HLK-PM03 (AC/DC) dies❌ Light freezes in last state — single weak link
Mains breaker off❌ Everything off (expected)

This is roughly as reliable as a dumb mechanical switch — modulo one AC/DC module.

Topology Decision: Variant A (switch physically toggles 220V)​

When the wall switch is "off", the lamp fixture is fully de-energized — same UX as a regular dumb switch.

Rejected alternatives:

  • B (always-on, MQTT-only toggle) — violates local-first (network latency on toggle, station outage breaks lights).
  • C (NC relay default ON) — inverted logic; ESP reset desyncs from physical state.

What MQTT Adds (post local-first)​

Network is not needed for basic on/off. What MQTT enables:

DirectionPurpose
switch → stationbutton_long_press, motion_detected, state_changed events for automations
light → stationstate_changed after boot, brightness telemetry
station → lightset_brightness (0–100%), set_cct (2700K–6500K mix across WW/NW/CW channels)

Single short presses stay fully local — never sent as commands.

The switch-light Preset​

The kit auto-creates automations from a preset. Useful presets that use MQTT:

  1. PIR → light with timeout — motion detected → if light is on, set brightness 100% and reset timer; no motion for N min → set brightness 0%
  2. Long press → night mode — button_long_press → set_brightness(30%) or cycle through brightness presets

Single press stays untouched (relay handles it directly).

See station/backend/domain → kits for how presets become automations.

Open Questions​

  • PIR behaviour when light is off — three options: (a) PIR passive, only publishes events; (b) PIR auto-closes the relay (motion → light); (c) preset config switch. Leaning towards (c) with default off.
  • Production form — hand-soldered prototype (THT) vs JLCPCB SMT.
  • Certification — for resale, EN 60669 (switches) and EN 60950 (PSU) apply. Not blocking for prototype.

Reference​