AkvaLink 💧

Battery-powered Matter pool & aquatic temperature sensor Single-SoC design on u-blox NORA-W40 (ESP32-C6, Wi-Fi 6 + Thread + BLE 5.3)

Multi-year battery life. Local Matter connectivity. No cloud, ever.

🌐 Live demo & landing page: stenmo.github.io/AkvaLink (available in English · Svenska — connect to a nearby sensor live over Bluetooth, right in your browser)

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Why AkvaLink?

Pool, spa, aquarium, wine cellar, or cold-storage temperature monitoring — environments where the temperature barely changes, but you want to know immediately if it does.

• 🔋 Years on 2× AA — adaptive sampling + Matter SED + threshold reporting
• 📱 Works with Apple Home, Google Home, Alexa — standard Matter sensor
• 🌐 No cloud — local Matter over Thread or Wi-Fi
• 💧 Waterproof probe — DS18B20 in stainless steel (10 m+ cable possible)
• 🛠 Open source — built on esp-matter, Apache-2.0 license

Hardware

Component	Part	Why
Module	NORA-W401 / NORA-W406	Wi-Fi 6 + Thread + BLE in one tiny module
MCU	ESP32-C6 (RISC-V @ 160 MHz)	Inside NORA-W40
Sensor	DS18B20 (stainless probe)	±0.5 °C, 12-bit (0.0625 °C steps), 1-Wire, ~$3
Power	2× AA alkaline (or 18650 Li)	~5–7 years realistic on 2× AA (Thread SED, pool conditions)*

Schematic (direct GPIO, default build):

                         ┌──────────────────────────────────────────┐
                         │       NORA-W40 / EVK-NORA-W40            │
  +3V3 ────────┬──────── │ GPIO15 (J15.4)  ← DS18B20 DQ 1-Wire      │
               │         │                                          │
              4.7 kΩ     │ GPIO9  (BOOT)   ← re-provision button    │
               │         │                   long-press 5 s →       │
DS18B20 ───────┘         │                   erase Wi-Fi, re-prov   │
  DQ ──────────────────► │                                          │
  VDD ────────────────── │ +3V3            ← future: battery ADC    │
  GND ────────────────── │ GND                                      │
                         │                     ┌──────────┐         │
  Battery (+) ──── R1 ───┤ ADCx (future) ◄─────┤ R1 / R2  │         │
  Battery (-) ──── GND   │                     │ divider  │         │
                         └─────────────────────┴──────────┴─────────┘

R1/R2 voltage divider (not yet populated): e.g. 390 kΩ / 100 kΩ scales 3.3 V full-charge to ≈ 0.68 V, safely within the ESP32-C6 ADC input range.

For long cable runs (> 5 m), a DS2482-800 I2C-to-1-Wire bridge variant is also supported (--clickboard build flag).

Quick start

# One-time setup (installs ESP-IDF + esp-matter in WSL, ~10 GB)
.\akvalink.cmd setup

# Build & flash (Thread variant — needs a Thread Border Router)
.\akvalink.cmd build
.\akvalink.cmd flash COM62

# Or build the Wi-Fi variant (no border router needed)
.\akvalink.cmd --wifi build

# Or the Wi-Fi AP variant — open "AkvaLink" hotspot + captive web page showing
# the temperature. No hub, no app, works on ANY phone (incl. iPhone).
# NOTE: an always-on SoftAP is NOT battery-friendly — this variant needs
# external (mains/USB) power.
.\akvalink.cmd --ap build

# Or the Wi-Fi station variant — joins your home Wi-Fi (provisioned once over
# BLE with the free "ESP BLE Provisioning" app), then serves the temperature
# page at http://akvalink-<last4mac>.local (found via mDNS, unique per device).
# Also publishes to MQTT for Home Assistant autodiscovery (default broker:
# homeassistant.local:1883), plus high/low temperature alerts on
# akvalink/<mac>/alert once you set a threshold (menuconfig → AkvaLink).
.\akvalink.cmd --station build

# Or just bench-test the DS18B20 probe (no Matter/BLE — logs temp every 30 s)
.\akvalink.cmd --sensor build

# Or the e-ink display receiver — listens for --espnow sensors' broadcasts
# and logs them (no e-ink panel driver yet). See docs/EINK_DISPLAY_PLAN.md.
.\akvalink.cmd --display build

# Or the ESP-NOW variant — deep-sleep broadcast, no hub, no provisioning,
# maximum battery life (receiver needs its own ESP32 sketch).
.\akvalink.cmd --espnow build

# Or ESPHome — native Home Assistant API, adopted + OTA-updated straight from
# the ESPHome dashboard. Builds with ESPHome directly, not akvalink.cmd:
esphome compile esphome/akvalink.yaml

Commission with the Apple Home, Google Home, or Alexa app — scan the QR code printed on the serial console at first boot.

📖 Full step-by-step: see GETTING_STARTED.md

Companion app (optional)

A native Flutter app (Windows/Linux/macOS/Android/iOS) shows live temperature over Bluetooth or Wi-Fi (finds a --station device on the LAN via mDNS) and one-click OTA-updates the device — same GATT/HTTP contract as the web page, no browser needed:

.\akvalink.cmd --app --run

📖 See app_flutter/README.md.

Battery life examples

For a heated pool at 28–29 °C with 0.25 °C report threshold. Leading with the realistic number for each cell: alkaline (AAA/AA) self-discharge and Li-ion (18650) calendar aging cap real-world life at roughly 5–7 years no matter what the draw-limited model alone predicts, so that cap is shown wherever the model overshoots it. CR2477 (lithium primary) has the best shelf life of the four and needs no such cap — its model figure already is the realistic one:

Battery	Thread SED	Wi-Fi (TWT)	Wi-Fi (disconnect)
CR2477 (1000 mAh)	~5 years	~6 months	~3.3 years
2× AAA (1200 mAh)	~5–6 years	~8 months	~4 years
2× AA (2800 mAh)	~5–7 years (model: ~12 years)	~1.8 years	~5–7 years (model: ~9 years)
18650 Li-ion (3400 mAh)	years, not decades (model: ~15+ years)	~2.2 years	years, not decades (model: ~11 years)

The italic (model: ...) figure is the theoretical, draw-limited ceiling — only shown where it's materially higher than the realistic number. Real measurement (PPK2/Joulescope) to replace "years, not decades" with an actual figure is on the roadmap.

See docs/POWER_AND_HARDWARE.md for the full analysis (DTIM strategies, TWT setup, sensor variants, schematic).

Project docs

• 📖 GETTING_STARTED.md — clone → build → flash → commission
• 📶 docs/CONNECTIVITY.md — Matter/Thread, Matter/Wi-Fi, BLE-only, Wi-Fi standalone + provisioning
• ⚡ docs/POWER_AND_HARDWARE.md — battery math, schematic
• ❄️ docs/WINTER_STORAGE_MODE.md — "drop it in the pool and forget it" mode
• 📺 docs/EINK_DISPLAY_PLAN.md — e-ink panel shortlist + integration plan
• 💧 docs/ENCLOSURE_DESIGN.md — Smart Float industrial design + mechanical details
• 📡 docs/RF_AND_ANTENNA.md — NORA-W40 antenna keep-out + over-water RF rules
• ✅ TODO.md — prioritised roadmap (power, smart reporting, e-ink, winter mode)
• ⚠️ KNOWN_LIMITATIONS.md — what doesn't work yet, honestly

Roadmap

• Matter Temperature Sensor over Thread (single-SoC, NORA-W40)
• Matter Temperature Sensor over Wi-Fi
• Adaptive sampling + threshold reporting
• Light sleep + DFS + flash power-down
• DS2482 Click board (long cable variant)
• BLE firmware update over the air (custom GATT over esp_ota, --ble variant)
• Standalone BLE GATT variant — live temperature direct-to-app, no hub (--ble)
• Live temperature in the browser over Web Bluetooth — on the landing page
• Wi-Fi AP variant (--ap) — open hotspot + captive web page, any phone incl. iPhone (needs external power)
• Wi-Fi station variant (--station) — BLE-provisioned, akvalink.local, Home Assistant MQTT autodiscovery, no hub
• ESP-NOW variant (--espnow) — deep-sleep broadcast, no hub, no provisioning
• ESPHome variant — native Home Assistant API, dashboard-adopted + dashboard OTA
• Native Flutter companion app (Windows/Linux/macOS/Android/iOS) — live temperature + one-click OTA
• Temperature alerts — high/low thresholds set from the browser or the app, stored on the device; the --station build publishes crossings to Home Assistant over MQTT
• 24 h / 7 d history — sparkline on the device's own page and in the app (Wi-Fi path; RAM-only, resets on reboot)
• Matter keepalive report so a dead-flat sensor isn't marked offline
• Real power measurement (Joulescope/PPK2) + deep sleep — see TODO.md
• E-ink display (big-digit, battery, trend) — --display build variant receives --espnow sensor broadcasts and logs them; e-ink panel driver still to come; see docs/EINK_DISPLAY_PLAN.md
• Wi-Fi 6 TWT integration in code (currently DTIM only)
• Battery voltage monitoring — firmware side is in (CONFIG_AKVALINK_BATTERY_ADC, off by default), but no board has the sense divider fitted, so the level reads as unknown
• OTA via Matter
• Production enclosure design (waterproof, IP67)

Origin & Credits

AkvaLink is a clean-room productisation of the companion/opencpu/nora-w40-thermometer/ NORA-W40 thermometer reference from u-blox, tracked at u-blox/u-connectMatter (that public repo now hosts prebuilt reference binaries; the source tree is internal to u-blox).

Built on:

• esp-matter (release/v1.5)
• ESP-IDF (v5.5.5)
• connectedhomeip (Matter SDK)
• u-blox NORA-W40 module (product page)

Contributing & security

• 🤝 CONTRIBUTING.md — how to build, test, and submit changes (KISS, battery-first, no cloud)
• 🔒 SECURITY.md — report a vulnerability privately (AkvaLink is a networked Matter device)
• 🔏 Code signing policy — how the Windows companion app is signed (free signing via SignPath.io)

License

Apache-2.0 — matches esp-matter and connectedhomeip.