Protect Your Family From 3D Printer Fumes With a $50 Air Purifier

I automated a $50 air purifier to protect my family from 3D printer fumes, starting automatically with every print and shutting off on its own when the air is clean.

1. Air purifier with a capacitive touch button (e.g., Levoit Core Mini (LAP-C161-WEU))
2. S9013 NPN transistor
3. 1 kΩ resistor between GPIO and the transistor base
4. 10 kΩ pull-down resistor to hold the GPIO pin low when inactive
5. Optional: LED with 470 Ω resistor as a visual status indicator
6. Oscilloscope (needed if another Air Purifier is used)
7. Raspberry Pi (e.g. Pi Zero 2W)

My 3D printer lives in a wooden & acrylic glass enclosure in my home office. My kids come in all the time. And for a while, I had been ignoring the smell. You know the one. That plasticky, slightly chemical odour that kicks in as soon as the print starts. I told myself it was fine. PLA is supposed to be safe, right?

Then I started reading a bit more about what actually comes out of these machines while they are running. That was enough to make me want to do something about it.

When plastic filament melts and gets deposited layer by layer, two things are released into the air. First, very fine particles, small enough to stay airborne for hours and get deep into the lungs. Second, chemical vapours from the heated plastic. Even PLA, which is often marketed as the safe, plant-based option, releases some of these compounds. ABS and PETG are worse.

An enclosure helps keep the heat in and improves print quality, but it also concentrates everything inside a small box. Every time you open it, that air goes straight into the room. If your kids are nearby, that is the moment I was most uncomfortable with.

Good ventilation helps, but I wanted something better. Active filtration, inside the enclosure, running automatically during every print.

I did not want to build a filter from scratch or buy some overpriced industrial unit. I wanted something that already works well, that someone else had already engineered properly, and that did not cost a fortune. A compact consumer air purifier with a proper HEPA H13 filter and an activated carbon layer fits the bill perfectly.

HEPA H13 captures the fine particles. Activated carbon absorbs the chemical vapours. Together they deal with both problems. Units like this are available from several brands in the 45 to 55 EUR range and are small enough to sit on the floor of a wooden enclosure without taking up much space.

I was initially worried that having the purifier at the bottom of the enclosure would not be effective. It turns out not to be an issue. These cylindrical units draw air in from all sides and push it out upward, which creates enough circulation inside the enclosure to filter the air properly, even from below.

The obvious approach is to just turn the purifier on when you start a print and turn it off when you are done. In practice, this never works reliably. Prints finish while you are in another room. You forget to turn it on. The machine is running and nobody noticed.

I wanted it to be completely automatic. Start a print, filter runs. Print finishes, filter keeps running for a few more minutes to clear the air, then shuts itself off. No manual steps, no forgetting.

The purifier I was using has a single touch button for power and speed control. Not exactly designed for external automation. But that turned out to be easier to solve than expected.

Most touch buttons on consumer electronics work by detecting a change in capacitance when you touch them. A small signal runs through the button surface, and the electronics notice when something conductive, like a finger, comes near it.

With an oscilloscope I could see exactly what the button was doing. The key finding: briefly connecting the button contact to ground produces the exact same effect as a finger press. The electronics cannot tell the difference.

So a single transistor, costing a few cents, can simulate a button press from a Raspberry Pi GPIO pin. Short press: next speed level. Long press (three seconds): power off. That is the entire hardware side of the project, plus a couple of resistors and an optional LED to show when the system is active. Total parts cost: under one euro, not counting the purifier itself.

My printer is managed by OctoPrint, running on the same Raspberry Pi that I used for the GPIO control. OctoPrint has a plugin called GCode System Commands that lets you define custom commands which execute shell scripts. These commands can be placed in OctoPrint's print event scripts.

The setup is straightforward:

1. When a print starts, a script runs that stops the purifier first (to get to a known state), then starts it at speed 2.
2. When a print finishes or is cancelled, a purge cycle runs: the purifier advances to speed 3 and runs for five minutes before shutting off automatically.
3. If a new print starts while the purge is still running, the purge is cancelled cleanly and the purifier restarts in its normal print mode.
4. If the connection to the printer is closed manually, the purifier stops as a fallback.

The five-minute purge after printing is the part I am most happy with. It means the enclosure is properly cleared before I open it, which is exactly when my kids are most likely to wander in to see what came out.

From a user perspective there is nothing to do. I start a print from OctoPrint and the rest happens by itself.

The smell is noticeably reduced. Not completely gone, but the difference is real and immediate. The room no longer accumulates that chemical odour during long prints. Opening the enclosure after the purge cycle has run is much better than it was before.

The automatic workflow has been reliable. The purifier starts every time, stops every time, and the five-minute cooldown runs without any input from me. The LED on the control board gives a quick visual confirmation that the system is active, which is a small but nice touch.

Total cost of the project: around 55 EUR for the purifier, plus components that cost less than a cup of coffee. The Raspberry Pi was already part of the setup.

Everything is published openly, including the Python control scripts, shell wrappers, circuit diagram, and full wiring and configuration instructions:

https://github.com/CBR2021Pi/octoprint-airfilter

The approach works with any compact air purifier that has a capacitive touch button. The specific timings depend on the device, but the circuit and software structure are reusable. If you have a 3D printer at home and people you care about breathing the same air, it is worth half an afternoon to set up.