FanCtrl3-Pro

FanCtrl3

A USB-powered controller for three 4-pin PWM fans, driven by the CPU temperature of a Proxmox VE host.

One USB cable to the host is all it needs — power, control and fan speed readings all go over it. The fan curve runs inside the controller, so a host reboot, a crashed service or a pulled cable never leaves the fans stopped.

Designed for small home servers and mini PCs running Proxmox: the machine sits in a closed cabinet, its own fan is not enough for the cabinet, and a set of quiet 120 mm fans should spin up only when the server actually works.

[!NOTE] FanCtrl3 is a hobby project, built in spare time. Updates may not come often — but ideas, questions and build reports are always welcome (see Contact and contributions).

Project status

[!WARNING] FanCtrl3 has not been tested on real hardware yet. Hardware testing is coming soon; this section will be updated with the results. Until the first boards have run for a while, treat this as a reviewed design, not a proven product.

Verified without hardware

Every push and pull request runs these tests on GitHub Actions.

Not tested yet

• Anything on a real board: soldering, the 12 V rail, the current limiter and its FAULT signal, real fan speeds from the tachometers, the DS18B20 probe, the LED, the watchdog, USB behaviour with and without a host.
• Power drawn from a real USB port with three fans at 100 %.
• The udev rule on a real Pico (2e8a:0005 is MicroPython's default ID).
• Printing and fitting the enclosure; the Lite mounting-hole positions.

Known issues

• AMD support (k10temp, zenpower) is tested only against simulated sensors so far — a report from a real AMD host is welcome.
• tests/test_main_smoke.sh depends on timing and can fail on a heavily loaded machine; run it again before looking for a bug.

Features

• Three 4-pin PWM fans, 25 kHz PWM and tachometer reading on every channel.
• Powered from USB only. An on-board step-up makes the 12 V for the fans; a TI TPS2553 current-limited switch limits the fan side to 465–570 mA — the budget of a USB 2.0 port — and reports an overload to the controller.
• Curve in the controller, temperature from the host. A small daemon on the Proxmox host sends the CPU package temperature (Intel or AMD) every 5 seconds; the controller applies a curve with hysteresis and ramping.
• Safe by default. No temperature for 30 s → fans at 100 %. A dead microcontroller → the output transistors switch off → fans at 100 %. A clean host shutdown → fans rest at 20 % instead of alarming.
• Ambient probe. A DS18B20 on a cable measures the air in the cabinet and raises the fans on its own above 40 °C (60 %) and 45 °C (100 %).
• Stall detection per fan, per-fan minimum duty and a calibrate command that measures it.
• Two variants, one firmware — see below.
• Host side needs nothing but Python 3's standard library, a udev rule and a systemd unit.

Two variants

Both use the same pinout and run the same firmware.

Lite — perfboard wiring drawing	Pro — PCB, top
Lite — enclosure	Pro — enclosure

How it works

 Proxmox host                                 FanCtrl3
┌────────────────────────┐   USB cable    ┌──────────────────────────────────────┐
│ CPU temp ─► fanctl     │  power + data  │ Pico: curve, hysteresis, failsafe    │
│             daemon ────┼───────────────►│  ├─ PWM ×3 ──► open collector/drain  │
│  TEMP 54.0 every 5 s   │◄───────────────│  ├─ tach ×3 ◄── fans                 │
│  STATUS, alarms        │                │  └─ DS18B20 ◄── ambient probe        │
└────────────────────────┘                │                                      │
                                          │ VBUS ─► TPS2553 ─► 12V boost ─► fans │
                                          │         (≈0.5 A)                     │
                                          └──────────────────────────────────────┘

The link is plain text over USB CDC — TEMP 54.0, STATUS, SET 1 40 — so it can be driven by hand from any terminal. Full protocol: docs/firmware.md.

Power budget

The whole controller lives on one USB 2.0 port, which is allowed to supply 500 mA. The design is sized for three low-power 120 mm PWM fans rated at up to 0.6 W each (for example Noctua NF-P12 redux-1300 PWM):

3 × 0.6 W = 1.8 W at 12 V → ÷ 0.85 converter efficiency + ≈ 0.15 W for the Pico ≈ 0.45 A from the port.

[!CAUTION] Fans rated above 0.6 W each will not fit this budget. The TPS2553 limits the fan side to 465–570 mA and reports FAULT, but the fans will not reach full speed. Check the rated input power of your fans before you build.

Getting started

1. Pick a variant and order the parts — docs/bill-of-materials.md.
2. Build the board — Lite or Pro.
3. Print the enclosure — docs/enclosure.md.
4. Flash the firmware — docs/firmware.md: MicroPython for RPI_PICO, then firmware/flash.sh.
5. Install the host side on Proxmox — docs/host-proxmox.md:

   sh host/install.sh        # as root on the Proxmox host
   fanctl status
   fanctl calibrate          # finds the lowest duty each fan still spins at

Repository layout

Documentation

• Hardware design — circuit description, pinout, design decisions
• Bill of materials — both variants, with suggested shop links
• Building FanCtrl3 Lite — perfboard assembly
• Building FanCtrl3 Pro — ordering the PCB and hand soldering
• Enclosure — printing and assembly
• Firmware — flashing, control behaviour, serial protocol
• Host software on Proxmox — installation and fanctl
• Development — regenerating the outputs, running the tests

Contact and contributions

Ideas, improvements, a better circuit, a build report or a question — all welcome. Open an issue on this repository or write to support@fractal8.eu. See CONTRIBUTING.md.

Support the project

FanCtrl3 is built in spare time. If it is useful to you, you can support its development through GitHub Sponsors — it helps pay for parts and prototype boards.

Licence

MIT — see LICENSE. This covers the hardware design files, the firmware and the host software.