An HVAC system is a handful of temperature sensors and a handful of things to switch. The awkward part is that the switching is mains, the sensing is millivolts, and the boiler already in the room has its own bus and will not tell you anything unless you ask it properly.

Havaxer™ is one board that does all three. Temperature sensors in, mains out, and an isolated eBUS adapter so it can read the equipment that is already there instead of duplicating it. An optional display, two buttons, and every screw terminal named and rated on the board itself.

You write the control logic. The board handles everything between your code and the plant.

None of that is peculiar to HVAC. Temperature in, mains out, a bus to listen to and a rail to run from is equally a greenhouse, a brewery, a pump house or a workshop. HVAC is where the board came from and what it was proved on, not where it stops.

What it does

• Reads temperatures - 5 or 6 inputs for ordinary 10 kΩ NTC thermistors. The same inputs take a dry contact, so a window switch or a float switch needs nothing extra.
• Knows whether a wire is live - isolated mains inputs, so you can confirm a pump or burner actually started rather than assuming it did.
• Switches mains two ways - relays for anything, including inductive and DC loads, and silent solid state outputs for what switches all day.
• Drives small things directly - 5 V outputs with a fuse and a flyback diode, so an external relay coil wires straight to the terminal.
• Talks to the boiler - a built-in, fully isolated eBUS adapter that draws no power from the bus at all.
• Runs from what the panel already has - USB-C, or 7-33 VDC in either polarity, or 7-28 VAC. About 2 watts.
• Shows you what it is doing - an LED beside every input and output, and an optional OLED with two buttons for local control.

Every capability is documented in full on the Features page: what it is, how it behaves, and where its limits are.

Choosing a model

Both boards do the same job. The 02 is bigger, has more of everything, and has a radio.

Take the 01 if the controller stands alone, the logic is yours, and you would rather be able to swap the microcontroller with your fingers than a soldering iron.

Take the 02 if anything needs to leave the building - monitoring, remote control, MQTT, a dashboard - or if you want more outputs than the 01 has.

Both share the same terminals, the same eBUS adapter, the same display and buttons, the same power options and the same reference firmware structure.

02

ESP32-C6, 6 temperature inputs, 2 mains inputs, 4 relays, 4 triacs, 2 signal outputs, twin IO, Wi-Fi. More details.

01

Socketed PIC, 5 temperature inputs, 1 mains input, 3 relays, 2 triacs, 1 signal output. More details.

How it is sold

Designed in Slovenia, manufactured by JLCPCB, inspected and tested here before it ships. Sold direct by e-mail or Telegram - no cart, no marketplace, no company behind it. Shipping is inside the EU only.

Every board is sold as-is and is not CE, FCC or UL marked. It switches mains, so it is meant for professional users, businesses, and technically skilled individuals - read Installation and safety before wiring one.

Hardware support is included with a purchase. Firmware support is not: the example application exists to demonstrate and test the board, and the control logic is yours to write.

Hardware issues are tracked in public - 01open_in_new, 02open_in_new - including the ones that are still open.