SolBus Ahaon — Resol VBus to WiFi Board (ESP32-C3)

SolBus Ahaon — 'a haon', Irish for one — the all-in-one board, designed in Ireland.

Get your solar thermal system into Home Assistant with one small board. SolBus Ahaon reads live data from your Resol / DeltaSol solar controller over VBus and sends it to Home Assistant via ESPHome. The ESP32-C3 is built in, so there's no separate ESP to wire up and no jumper leads. Connect two wires, plug in USB-C, and you're logging.

What's new in V2

• Works with the standard ESPHome VBus config. The VBus signal is now corrected in hardware, so you use a plain rx_pin: GPIO3 with no inverted: true workaround. The example configs from the ESPHome VBus docs work as written.
• Power / status LED on from the start. The LED lights as soon as the board gets power, even before it's flashed, so you can see at a glance that it's alive. Once ESPHome is running, it works as a proper status light and blinks if something goes wrong.
• Marked "v2" on the board, so you always know which version you have.

What you see in Home Assistant

• Collector, tank and return temperatures (all Pt1000 sensor readings)
• Pump / relay status and speed
• Operating hours, heat quantity and system status, where your controller reports them

Features

• All-in-one: VBus front-end and ESP32-C3-MINI-1 on a single board
• Native USB-C: power and flashing over the same cable, no USB-serial adapter needed
• Screw terminal for the two VBus wires, so no soldering is required
• BOOT / RST buttons for easy flashing and recovery
• Status LED: on at power-up, controlled by ESPHome for status and error indication
• ESPHome ready: works with ESPHome's built-in VBus component
• Read-only: it listens to VBus and never writes to your controller

Compatibility

Works with any Resol VBus controller. If your controller has VBus terminals (often 9/10), this board will read it. That includes the rebadged versions: Resol, DeltaSol, Viessmann (Vitosolic), Firebird, COSMO, Caleffi (iSolar), Sonnenkraft, Kingspan, Joule, Citrin Solar, De Dietrich, Wagner, Kioto, Apricus, Thermann, Dux.

• Native ESPHome models (just select the model): DeltaSol BS Plus, BS 2009, BS/2 (DrainBack), C, CS, CS2, CS4, CS Plus.
• Other models such as the BS/4, BS/2 HE, E and SLL are read fine by the hardware but need a short custom ESPHome config. If you have a BS/2 HE, I can send you my working config on request.

Not sure about your controller? Message me before ordering with the model name or a photo of the label, and I'll tell you straight whether it's supported.

What's in the box

• 1× SolBus Ahaon board (model VBUS-C3-V2)

You supply a USB-C cable, a 5V USB power adapter, and two wires to your controller's VBus terminals.

Specifications

• MCU: ESP32-C3-MINI-1 (WiFi 2.4 GHz)
• Power: 5V via USB-C
• VBus input: 2-pin screw terminal, receive-only, on GPIO3
• Status LED: GPIO10 (via MOSFET, on by default)
• Front-end: 1N4148 bridge with LM339 comparator. The VBus and ESP share a ground reference, which is standard for a receive-only tap on a low-voltage SELV bus.

About this board

SolBus Ahaon is an open-hardware developer board for Home Assistant and ESPHome users. It's built on the open-source VBus community work, with credit to the original authors.

Safety: Power only from a 5V USB supply. Connect only to low-voltage VBus data terminals, never to mains or relay outputs. For indoor, dry use. At end of life, dispose of as electronic waste (WEEE).

Manufacturer: SolBus, Dublin, Ireland. solbus.ireland@gmail.com

RESOL and VBus are trademarks of RESOL – Elektronische Regelungen GmbH. SolBus is not affiliated with RESOL.

Orders ship from Dublin, Ireland via An Post, usually within 1–2 working days. Standard Post is untracked.

Typical delivery times: Ireland 1–3 days, UK and EU 1–2 weeks, Canada/Australia/NZ 2–3 weeks.

EU and Northern Ireland orders have no customs charges. Orders to Great Britain and outside the EU are sent with a customs declaration.