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README.md

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+# Voron filament dryer
+
+Arduino Nano firmware for a chamber dryer with four SHT31 humidity/temperature sensors, PID heater control, and PWM fan mixing.
+
+## Pinout (Arduino Nano)
+
+All settings below are defined in `include/config.h`.
+
+| Signal | Nano pin | Notes |
+|--------|----------|-------|
+| I2C SDA | A4 | Shared bus (Wire) |
+| I2C SCL | A5 | Shared bus (Wire) |
+| TCA9548A mux | I2C `0x70` | 8-channel I2C multiplexer |
+| SHT31 sensors | Mux channels 2, 3, 4, 5 | One sensor per channel |
+| SHT31 address | `0x44` | ADDR pin low; use `0x45` if ADDR is high |
+| Fan | D5 | 24 V fan via N-channel MOSFET (hardware PWM) |
+| Heater | A2 | Solid-state relay (burst control) |
+
+USB serial: **115200 baud**.
+
+## Dev setup
+
+### PlatformIO
+
+This repo uses the PlatformIO CLI (see `.vscode/tasks.json`). If PlatformIO is already installed under `~/.platformio/penv/`, use that directly — you do not need to run the web installer again.
+
+```bash
+~/.platformio/penv/bin/pio --version
+~/.platformio/penv/bin/pio run              # build
+~/.platformio/penv/bin/pio run -t upload    # flash
+~/.platformio/penv/bin/pio device monitor   # serial monitor
+```
+
+On Arch Linux / CachyOS, install via the package manager if you prefer:
+
+```bash
+sudo pacman -S platformio
+```
+
+If upload cannot find the port, add to `platformio.ini`:
+
+```ini
+upload_port = /dev/ttyUSB0    ; or /dev/ttyACM0, or a /dev/serial/by-id/... path
+monitor_port = /dev/ttyUSB0
+```
+
+List available ports:
+
+```bash
+ls -la /dev/serial/by-id/
+```
+
+### Serial port permissions (Linux)
+
+| Distribution | Group for serial access |
+|--------------|-------------------------|
+| Debian, Ubuntu, Raspberry Pi OS | `dialout` |
+| Arch Linux, CachyOS | `uucp` |
+
+```bash
+# Debian / Ubuntu / Pi
+sudo usermod -aG dialout $USER
+
+# Arch / CachyOS
+sudo usermod -aG uucp $USER
+```
+
+Log out and back in after adding your user to the group.
+
+## First run
+
+1. Flash firmware and open the serial monitor at 115200 baud.
+2. Confirm `TCA9548A detected` and four valid sensor channels (`ch2`–`ch5`).
+3. Run PID autotune once per physical unit (values are stored in EEPROM):
+
+   ```
+   target 0
+   autotune 45
+   ```
+
+4. Start drying:
+
+   ```
+   target 55
+   ```
+
+Send `help` over serial for all commands (`target`, `fan on/off`, `log on/off`, `status`, `pid`, etc.).
+
+## Raspberry Pi logging
+
+Optional CSV capture over USB is documented in [pi-instructions.md](pi-instructions.md).