Two documented builds for the in-vehicle BLE→WiFi bridge in ARCHITECTURE.md. They differ mainly in antenna strategy, and the right pick depends on where you mount it.
The bridge has two radios to keep happy: BLE to the control box and WiFi to a network. How much either one matters depends first on your network topology, then on where you mount the package.
Onboard network (van/RV/boat) — the easy case. If the vehicle has its own router + local WiFi (e.g. a Starlink/5G uplink) and Home Assistant runs onboard, then both radios are short, always-on, local hops. WiFi stops being a design variable — even a PCB-antenna board reaching your own AP across the vehicle is trivial — so pick on packaging alone (Option B is a great fit). The antenna tradeoff in the table below only bites when the bridge must reach an external/home AP intermittently (e.g. a Jeep parked in the driveway).
If you do depend on an external AP, where you mount the package decides which radio is the hard one:
| If you're… | Pick | Because |
|---|---|---|
| mounting away from the control box, or want to place the antenna freely | A. Olimex ESP32-GATEWAY-EA | external U.FL whip you can route to the best spot — helps both BLE and WiFi |
| mounting the package on/at the Auxbeam control box | B. Kincony KC868-A4 | 12 V-native, screw terminals, case, ESPHome-proven; BLE is solved by proximity — you just plan WiFi |
With an external AP, mounting on the control box makes BLE a non-issue (the ESP is inches from the module) but pins the Kincony's PCB antenna to the control box's location, so WiFi becomes the variable. See Option B's WiFi notes. (On an onboard-network van, skip that concern entirely.)
A vehicle rail sits ~12.6 V at rest, ~14.4 V charging, with load-dump transients far higher. Regardless of board, put this in front of the input:
- Fuse at the tap (1 A blade fuse + holder) — protects the wiring, not the board.
- Reverse-polarity — SS34 Schottky in series (simple, ~0.4 V drop) or a P-FET ideal-diode.
- TVS clamp to ground — SMBJ16A (16 V standoff so it's idle at 14.4 V; ~26 V clamp). Confirm your regulator/board input tolerates the clamp voltage; if its input spec is strict, add a wide-input pre-regulator (below).
- Common ground to vehicle chassis / panel ground.
With solar + a large battery, constant-on is fine — draw is tiny (see Power budget). Want it to sleep with the vehicle? Feed the front-end from an ignition-switched circuit, or add deep-sleep logic.
Best when the package sits away from the box, or you want to route the antenna to a good spot. The ESP32-WROOM-32UE routes RF to a U.FL connector + external 2.4 GHz whip — the flexible-placement choice, and it helps WiFi as much as BLE.
Order the
-EAvariant (WROOM-32UE + external antenna). The plain-Ehas a PCB antenna and defeats the reason to pick this board.
flowchart LR
BATT["12V rail\n(solar + battery)"] --> FE["front-end\nfuse + SS34 + SMBJ16A"]
FE --> BUCK["wide-input buck\nRecom R-78E5.0-1.0\n(6.5–28V → 5V)"]
BUCK -->|5V| BOARD["Olimex ESP32-GATEWAY-EA\nUSB-C 5V in → onboard 3.3V"]
BOARD --> UFL["U.FL → external 2.4GHz antenna"]
UFL -.BLE.-> BOX["panel control box"]
UFL -.WiFi.-> HOUSE["home network"]
| Part | Suggested specific | Notes |
|---|---|---|
| MCU board | Olimex ESP32-GATEWAY-EA (~€17) | Ethernet onboard is unused — leave it disabled |
| Enclosure | Olimex plastic box (~€8) or IP54 box | keep the antenna outside the box |
| Antenna | 2.4 GHz U.FL/IPEX whip (usually included with -EA) |
mount in open air |
| Buck | Recom R-78E5.0-1.0 (6.5–28 V→5 V) or Traco TSR 1-2450 | 28 V ceiling swallows the charging rail; TVS only catches big spikes |
| + front-end | fuse / SS34 / SMBJ16A | see above |
Power: buck 5 V → the board's USB-C (onboard LDO makes 3.3 V; don't also plug in USB).
ESPHome: board: esp32dev (or esp32-gateway); the WROOM-32UE hardwires RF to U.FL — no config.
The least-fuss build: ESP32-WROOM-32, 12 V-native input, screw terminals, opto-isolated inputs, an optional plastic shell, and a strong ESPHome track record ("flashed ESPHome — integration is native and rock solid"). Mounted on the Auxbeam control box, BLE is trivially solved by proximity; you'll ignore the onboard relays.
flowchart LR
BATT["12V rail\n(solar + battery)"] --> FE["front-end\nfuse + SS34 + SMBJ16A"]
FE -->|12V| BOARD["Kincony KC868-A4\n12V in → onboard regulator"]
BOARD --> PCB["PCB antenna (fixed)"]
PCB -.BLE (inches).-> BOX["panel control box"]
PCB -.WiFi (the variable).-> HOUSE["home network"]
| Part | Suggested specific | Notes |
|---|---|---|
| MCU board | Kincony KC868-A4 ($38 PCB; bundles add case + PSU) | 4 relays unused; opto inputs could be handy |
| Enclosure | Kincony plastic shell (bundle E/G) | |
| Power | feed 12 V directly through the front-end | no 5 V buck needed — a plus vs Option A |
| + front-end | fuse / SS34 / SMBJ16A | verify the board's input tolerance covers 14.4 V; if it wants a regulated 12 V, add a wide-input buck (e.g. Recom R-78 12 V, or a 9–36 V→12 V industrial buck) |
ESPHome: widely used on the KC868-A4; use Kincony's published pin map for its I/O. The BLE-client
portion of switchpanel-bridge.esphome.yaml is unchanged — keep
framework: esp-idf for ble_client.ble_write.
Only relevant if the KC868 must reach an external/home AP. On a van/RV with an onboard AP a few meters away, WiFi is a non-issue even with the PCB antenna — mount wherever is convenient and skip this.
For the external-AP case, with the package on the control box (often deep in engine-bay metal) and a fixed PCB antenna, WiFi is the link to design around, not BLE. Options, roughly in order:
- Improve the AP side, not the vehicle. A garage/driveway-facing 2.4 GHz AP or a mesh node near where you park is the highest-leverage fix (2.4 GHz penetrates better than 5 GHz — make sure the SSID is broadcast on 2.4). A directional antenna aimed at the parking spot helps further.
- Orient the board so its antenna end faces outward — toward a body gap, plastic panel, or the cabin — rather than buried against the metal box or block.
- Lean on graceful reconnect. ESPHome auto-reconnects and the panel state re-syncs on reconnect (FFF2), so intermittent WiFi degrades to "updates when in range," not broken control.
- External-antenna variant (if offered). If Kincony lists a WROOM-32U / U.FL version of the A4, take it and you get Option A's antenna flexibility with Option B's packaging. Otherwise the PCB antenna is the WiFi limiter (a module swap to WROOM-32U is possible but advanced).
ESP32 with WiFi + BLE active averages ~100–160 mA @ 5 V (~0.5–0.8 W) → ~60–80 mA from 12 V. Over a week parked that's a few Wh/day — noise against a kWh-class battery with solar. No deep-sleep needed unless you want it.
This bridge commands high-current vehicle circuits — some may drive winches or other momentary/high-consequence loads. Keep those out of any automation (or manual-only). The wired dash panel and RF remote remain independent overrides. No warranty; use at your own risk.
The LILYGO T-CAN485 is neat and cheap with an onboard 5–12 V buck, but that input window is under-rated for a charging vehicle (~14.4 V) and it has no external antenna — fine on a bench, wrong stressors here. The two builds above cover the useful ends of the tradeoff: A for antenna flexibility, B for turnkey packaging when you mount on the box.