Fan switch

hw-fan-switch

A small, wirelessly-controlled 12 V DC fan switch. It drives a fan with a variable PWM duty cycle and is controlled over a BLE long-range radio link, making it part of the Bleriot node network.

The board is built around a Puya PY32F003 Cortex-M0+ microcontroller with a PAN211x radio, and the firmware is written in Go and compiled with TinyGo.

Features

• Variable-speed fan control via hardware PWM (TIM14_CH1 on PB1).
• 50 kHz PWM carrier, above the audible range to avoid switching noise.
• Configurable low-speed handling:
  • Low-duty threshold — below this duty the fan is treated as stopped and the output is forced to 0.
  • Low-duty kickstart — a brief higher-duty pulse to overcome fan stiction when starting at low speed.
• Wireless control and telemetry over the PAN211x BLE long-range link.
• Yellow status LED is steadily on while the hub is online and flashes briefly once per second while offline.
• Device identity, radio settings, and configuration are owned by the site inventory and baked into each firmware image at build time.

Repository layout

Hardware

The status LED is active high. A successfully decoded hub packet keeps the node online for five seconds. While online the LED remains on; after the timeout it follows BleRiot's 200 ms on, 800 ms off heartbeat until another packet arrives.

The KiCad project lives in board/, with fabrication outputs (Gerbers, BOM, positions) under board/production/.

Firmware

The firmware is the importable fanswitch package. Its TinyGo implementation exports Run, while fw/spec exposes Config, the register table, chip, and a typed build/flash profile. BleRiot generates a private external package main inside the deployment module and calls Run with that instance's baked identity and configuration. Nothing is generated in this repository for a deployment build.

Prerequisites

• TinyGo
• pyOCD for flashing and RTT logging
• arm-none-eabi-objdump (optional, for disassembly)

Clone with submodules:

git clone --recurse-submodules https://github.com/burgrp/hw-fan-switch.git

Build and flash

Build deployment firmware from the authoritative site inventory. For the AGC checkout and its basement.fan instance:

cd /home/paul/git/agc/bleriot

# Inspect the generated entry point without writing it
go run . node gen --name basement.fan

# One-time: install the target CMSIS pack
go run . node install-pack --name basement.fan

# Generate the private entry point and build image.elf
go run . node build --name basement.fan

# Generate, build, flash, and open RTT
go run . node build --name basement.fan --flash --rtt

# Open RTT without flashing
go run . node rtt --name basement.fan

The bleriot node commands resolve the selected inventory instance. node build generates its identity and Config under that deployment's private .bleriot directory, then builds this module using the profile carried by spec.Type. The deployment pins the firmware version in go.mod; it does not carry fan-specific build flags. This repository's Makefile contains optional aliases for fw/cmd/dev.

Configuration

The inventory Config (see fw/spec/spec.go) controls runtime behaviour:

Control interface

The device exposes a single register over the Bleriot network:

Writing duty updates the fan speed; the hub's next scheduled GET observes the new value. A NULL write stops the fan. Reading returns the current duty.