BWG840x gateway firmware: BLE to Wi-Fi, built in 30 minutes

The board is a Fanstel BWG840x. Nothing here is board-specific, and the same path works for any nRF52 and ESP32 pair joined over UART.

How fast, from a written spec?Under 30 minutesOn the video, with the developer approving each step.

How many chips from one spec?TwoAn nRF52840 scanner and an ESP32 uplink, joined over UART.

What did it catch over the air?36 on the air, 0 receivedThe bug the logs could not show, before the fix.

Is it CRA-checked?Same sessionSBOM, CVE scan, posture, and the top finding fixed.

Board Fanstel IOT-BWG840-V1Silicon nRF52840 with a power amplifier, ESP32-WROOM-32DVerified 11 August 2026, NCS 3.3.1 and ESP-IDF 5.5.4

From the spec, the agent planned the architecture, wrote and built both codebases with their real toolchains, corrected its own build errors, flashed both chips, and verified the result on the live board. The developer approved every plan, build and flash. Nothing ran unattended.

The hardware

A Fanstel BWG840x gateway in its black enclosure with the external antenna fitted and two status LEDs on the front — The BWG840x as it ships

A Fanstel BWG840x taken apart: the back cover, the enclosure with the board inside and its external antenna, and the board itself with the nRF52840 module and the ESP32 module each outlined and labelled — Opened: the nRF52840 radio side and the ESP32 uplink side

Two chips on one board. The nRF52840 scans and forwards every advertisement over a framed UART link. The ESP32 filters, publishes to MQTT, and serves its own dashboard. The agent already holds the board’s pins, the power amplifier’s control lines and the LED table, so the prompt names the product, not the wiring.

The prompt

The spec used in the video, less the hardware context the agent now carries for this board. Adapt the behaviour to your own product and run it.

Build a production-grade BLE-to-MQTT gateway on my Fanstel BWG840 board
(nRF52840 + ESP32). Two firmware projects.

ESP32 (ESP-IDF):

1. First boot (empty NVS) → WiFi Access Point "BWG840-XXXX" (XXXX from MAC)
   with a web dashboard to configure: WiFi credentials, MQTT broker
   (host, port, user, password, topic prefix), sensor MAC whitelist,
   and payload mode (see 4).
2. "Save & Reboot" → persist all to NVS, reboot into Station mode.
3. Station mode: connect WiFi + MQTT, dashboard stays reachable at
   http://bwg840-XXXX.local (mDNS) with tabs: Status, Config, Live Logs.
4. Receive BLE advertisements from the nRF52840 over UART, filter by
   MAC whitelist, publish to MQTT (topic per device MAC).
   Two payload modes, selectable in the dashboard:
   - RAW: JSON with mac, rssi, timestamp, raw advertisement hex
   - PARSED: decode standard BLE AD structures (device name, TX power,
     manufacturer ID, iBeacon, Eddystone, service data).
5. WiFi fails repeatedly → automatic fallback to AP setup mode.
   Never brick on bad credentials.
6. Dashboard UI: professional product quality, dark theme, card layout,
   live status badges, auto-scrolling log view, usable from a phone.
   ALL assets embedded in firmware, no external CDN, fonts or scripts.

nRF52840 (nRF Connect SDK / Zephyr):

7. Continuous BLE scanner: forward ALL advertisements (MAC, RSSI, raw
   payload) over UART. No filtering here; the ESP32 filters.
8. Button (10-second hold) → send "config reset" frame to ESP32 →
   ESP32 returns to AP mode with the old config pre-filled.
   Acknowledge the reset: both LEDs flash 3× together.

Both sides:

9. Framed UART protocol: start byte, length, CRC. Include a status frame
   so both chips know the global state, for the LED table.
10. LED status: blue = mode and connectivity, red = problems only.
    Implement the exact state table I give you.
11. Watchdogs (hardware + task), reconnect and backoff everywhere,
    proper prj.conf + sdkconfig, clean module structure.
12. Logging discipline: INFO everywhere, DEBUG only per module, only
    when investigating, rate-limited. No per-advertisement printing.
13. When done and I confirm: generate GATEWAY-GUIDE.md, a user manual
    covering LEDs, button, dashboard, MQTT topics, payloads and reset.

Work step by step: scaffold both projects, then build, flash, and verify
each stage on the real hardware using the live logs.

The series, in three chapters

The buildBoth projects scaffolded, built, flashed and verified live. The episode above.

The bug the code could not showClean logs, a tag five centimetres from the antenna, nothing received. Found over the air.

CRA readiness on the firmware just builtAn SBOM, a ranked CVE scan and a posture check, then the top finding fixed and rerun clean.

The full playlist, or the one-minute cut.

Reproduce it yourself

You need Adsum IoT Coder, the nRF Connect SDK, ESP-IDF, and a Fanstel BWG840x or any nRF52 and ESP32 pair joined over UART. No board? Run the agent on the bundled samples with the free tier.

Open an empty folder

Install the extension and open the panel.

Paste the spec

Adapt it to your board and product. Review the plan before any code is written.

Approve the builds, then the flashes

Both projects, corrected as it goes, then flashed and verified live.

Go further

3-layer debug for anything that works on paper and not on the air. CRA readiness once it is worth protecting.

Get started

How it works

What it does

Supported hardware

Build on partner open hardware

Reference

About

BWG840x gateway firmware: BLE to Wi-Fi, built in 30 minutes

The hardware

The prompt

The series, in three chapters

Reproduce it yourself

​The hardware

​The prompt

​The series, in three chapters

​Reproduce it yourself

The hardware

The prompt

The series, in three chapters

Reproduce it yourself