ControlUnit

Raspberry Pi–based control and data-acquisition system for a plasma laboratory. Logs vacuum and plasma parameters, controls gas flow via MFCs, and runs a closed-loop PID on plasma current. Built and operated by one principal developer over six years, with contributions from students and lab-mates passing through.

The box exists. It sits in a multi-chamber plasma lab. It is used today.

Current status

Function	State
ADC acquisition via I²C (AIO-32/0RA-IRC, 10 Hz)	live
MFC gas control — H₂ + O₂ via DAC8532	live
Plasma current PID via galvanically isolated MCP4725	live (Apr 2026)
GPIO sync signal for external loggers (QMS, others)	live
Kikusui LAN voltage/current recording	optional, timestamped CSV with Qt and full WebUI readouts; setup
Membrane temperature control via MAX6675 + SSR	dormant — migrated to NI/Windows

Hardware: Raspberry Pi 4 (8 GB) + custom PCB. Runs on-rig; also boots on Windows/macOS with dummy hardware stubs.

Quick start

On the lab Pi:

python -m controlunit.main

pigpiod is started automatically. GPIO access requires the daemon to have been started with appropriate permissions — on the rig this is handled by controlunit/start_gpio.py.

Off-rig (Windows/macOS — GUI only, no hardware):

python -m controlunit.main

Missing hardware libraries (pigpio, smbus, RPi.GPIO, spidev) are automatically replaced with no-op stubs from controlunit/devices/dummy.py.

Web view

Add --web and the same process also answers a browser, so the rig can be read from a laptop on the lab network:

python -m controlunit.main --web --host 127.0.0.1 --port 4187

It listens on loopback and port 4187 unless told otherwise, and it is read-only: a Lab page showing this service, the PIHTI journal and the PIHTI vacuum diagram with the state of each, plus GET /api/health for the two neighbours to read back. The neighbours' addresses come from a Neighbours: block in the machine-local ~/.controlunit/settings.yml, which this repository never carries. Without --web nothing about the program changes.

Documentation

Full documentation is at https://queezz.github.io/ControlUnit/

Page	Contents
Home	Overview and navigation
Archaeology	Forensic reconstruction of the full codebase history — primary technical reference
Qt Threading	Thread ownership, data flow, and shutdown safety diagrams
Channel Map	ADC channels, signal names, conversion functions
Related Projects	Ecosystem: echelle_spectra, pihtivacuum, TemperatureControl, tclogger

Hardware documentation lives in the lab-wide knowledge base: aklab-howto.

Repository structure

controlunit/        Python package — acquisition, control, UI
  devices/          per-device worker threads + chip drivers
  ui/               pyqtgraph docks and widgets
  settings.yml      channel map + conversion function registry (canonical)
docs/               MkDocs source
  Archaeology.md    primary historical document
archive/pdoc3/      legacy pdoc3-generated HTML (2022 snapshot, preserved)
images/             screenshots and physical box photos
tests/              minimal CI tests
examples/           scratch notebooks from development

Screenshots

Controls	Settings

Front panel	Back panel

Historical note

This codebase has accreted over six years: a 2020 monolithic worker template-copied from an earlier spectrograph application (echelle_spectra), extended by students, gradually refactored during experimental downtime, and still running in the lab. The full story — contributor history, threading evolution, design decisions, dormant capabilities, and ecosystem context — is documented in Archaeology.md.