Open-source air quality sensors for 50 schools

A classroom nobody can measure

Two winters ago a science teacher in Salford asked us a question we could not answer: how bad is the air in her classroom? Thirty-one children, one window that has been painted shut since the nineties, and a main road forty metres away. The council monitors the road. Nobody monitors the room.

Commercial monitors start at £600 per unit and lock their data behind a subscription. For a school running eleven classrooms that is a non-starter, and it is exactly the kind of school that most needs the numbers. So we spent fourteen months building the cheap version instead.

What we have already built

The Northgate AQ2 is a wall-mounted sensor that reads particulates, carbon dioxide, temperature and humidity, logs to a local server and shows a traffic-light strip that a nine-year-old can read from across the room. It costs us £42 in parts, takes eleven minutes to assemble and comes apart with one screwdriver. Twelve prototypes have been running in three Manchester schools since March without a failure.

• Hardware is finished — revision C boards came back from the fab in June and passed a four-week burn-in.
• The firmware, board files and enclosure model are already published under a permissive licence.
• Three schools have run the prototypes for a full term and helped us redesign the display.
• A teacher pack maps every reading onto the KS3 science curriculum, so the sensor becomes a lesson rather than a gadget.

What your money actually buys

This campaign funds fifty complete installations. We are not funding salaries — the studio covers those from workshop membership fees.

• £21,000 — 500 sensor units Ten per school, at £42 in components. Boards are panelised in one production run to keep the unit price down.
• £8,400 — Assembly and calibration Every unit is co-located for 48 hours against a reference-grade monitor before it ships. This is the step cheap sensors skip.
• £6,200 — Enclosures and mounting Injection-moulded cases instead of printed ones, because printed cases warp above radiators.
• £5,900 — School servers and installation days A low-power server per site plus two engineers on the road for ten weeks.
• £4,000 — Teacher packs, printing and a year of support Curriculum materials, a printed maintenance card in every box, and someone to answer the phone.
• £2,000 — Platform fees and payment processing Listed openly because it is real money and pretending otherwise helps nobody.

The children opened the window because the strip went amber. Nobody told them to. That is the whole point of the project in one sentence.

Who we are

Northgate Maker Studio is a member-run workshop in Ancoats with about ninety members — engineers, teachers, two retired instrument makers and a lot of students. Priya Raghunathan, who leads this project, spent nine years designing industrial sensing equipment before deciding that the interesting version of the job was the one that ended in a classroom. Everything we design is published; you can build an AQ2 yourself today without giving us a penny, and several people already have.

Risks and challenges

The honest risks are supply and time. Particulate sensors come from a small number of suppliers and lead times have moved between six and twenty weeks in the last year; if they stretch again, installations slip into the spring term rather than the autumn one. Injection-mould tooling is a single up-front cost and if the first tool is wrong we lose about three weeks correcting it. We also depend on schools finding staff time for a half-day install, which in practice means working around exam weeks. None of these risks stop the project; they move the finish line by a term at worst, and we will say so publicly the moment a date changes.