Hi y’all,

I'm Ian van Mourik a Product Designer from the Netherlands. This instructable is a brain child that I just had to share with the world. Bad air quality causes various health problems and purification solutions are often complex and expensive. The solution is an open source no nonsense air purifier: the OPEN AIR!

This instructable is based on my first experimental prototype of the OPEN AIR.

It’s meant to be a platform to build upon and improve. My personal goal is to test and improve the design and effectiveness. Collectively we can provide new and better solutions. The modular filter design makes it possible to change and test different kind of filters.

This Design is based on a carbon type filter in collaboration with two pressure optimized 120mm 12v PC fans. It´s controlled by an Arduino with a gas sensor and a LED panel for subtle visual feedback.

If you decide to build your own OPEN SOURCE AIR PURIFIER, be ready to roll up your sleeves, because this won't be an easy one. It will include laser cutting, 3D printing, prototyping, soldering, programming and a lot of other bits and bobs. It will be an advanced instructable. But don't let it scare you, because the reward is big, very big! Like thousands cubic meters of fresh pure clean air big.

Good luck!

Bill of materials:

1. Housing

  • 6 sheets (700x400mm) 3 mm multi-plex
  • 3 mm clear plexiglass
  • About 500 gram of 3D printer filament

2. Electronics

  • Arduino NANO v3
  • 5x 3mmm LED bright white
  • 2x 120 mm 12v fans (pressure optimized)
  • 5x LED resistors
  • Voltage controller 12v in, 5v out
  • 12v power supply (1.5A+)
  • MQ 135 gas and smoke sensor
  • Prototyping board
  • 2 pin connectors
  • 5 pin connectors
  • Wires

3. Air Filter

  • Activated carbon
  • Fine dust filter

Tools and extra's:

  • 3D Printer
  • Laser cutter
  • Soldering iron and Tin

  • Electrical tape
  • Screw driver
  • Nippers
  • Brush
  • Varnish or some other paint

  • Multi-meter
  • Sandpaper
  • Wood glue
  • 4x M3 x 40 bolts
  • 2x M3 x 15 bolt
  • Spacer
  • a PC

  • and a healthy brain

Total cost: 70 euro

Step 1: Fabrication Frame

Picture of Fabrication Frame

The first
step is to fabricate all the parts of the OPEN AIR, beginning with the laser cut wooden frame. I unfortunately do not own a laser cutter :(. But lucky there is a FABLAB nearby: #stadslabrotterdam.

I used 3mm triplex birch wood sheets, birch wood is ideal for laser cutting because it is very soft, and it's cheap witch is always good. Speed and power settings for the laser cutter are depended on the type of wood and machine you are using. Ask the FABLAB crew for help if you are not sure.

You will need one top and one bottom piece, 22 regular ribs, 1 wooden rib with the cutouts for the gas sensor, 1 Plexiglas rib for the LED and a couple of assembly tools.

For the LED rib I used 3mm clear blue Plexiglas which I roughly sanding in a vertical direction. Roughing up clear Plexiglas diffuses the light causing it to light up. Feel free to experiment!

After cutting check everything with a quick test fit, NO GLUE! I would highly recommend cover the wood with some kind of varnish or paint to prevent the wood from warping over time. So sand it down and do whatever you desire. I used heavy duty varnish for a old and kind of dirty finish.

Step 2: Fabrication 3D Printed Parts

Picture of Fabrication 3D Printed Parts

There are 4 printed parts totaling roughly 24 hours of printing time.

The coupler for the 120mm fans, the coupler for the filer and the filter itself are all printed in the same direction with the same settings. Depending on the printer, the tolerances on the tread can be a bit too tight and may require some sanding to make it fit. All the holes for the M3 bolts should be self-tapping.

Step 3: Electonics

Picture of Electonics

The open air is made to be
completely autonomous. It has a gas sensor to measure the air quality and a LED panel for visual feedback. My PCB and code is made so there are 3 options:

Clean air: fans and LED are off.

Dirty air: The fans spin near client (speed can be adjusted with a 1K ohm variable resistor) and the LED's breaths slowly in an upwards motion.

Gross air: Fans speed up to maximum and the LED's breaths fast in an upwards motion.

The basic setup of the PCB is made with two relays for the 2 fan speeds. One is direct 12v for full speed and the other is guided though variable resistor.

To provide the Aruino with 5v while using a 12v power supply I used a couple of voltage regulators. This creates a 5v rail for the Arduino and sensor, a 12v rail for the fans and a common ground rail.

The 5 3mm LED's can be glued inside of the cutouts in the Plexiglas. All LED's have the same ground wire, and the positive anode sides will be connected to the Arduino PWM output ports.

LED to Arduino pin connections with resistors. From top to bottom.

  • pin 3 - 100 ohm
  • pin 6 - 340 ohm
  • pin 9 - 220 ohm
  • pin 10 - 100 ohm
  • pin 11 - 100 ohm

The resistance varies depending on the thickness of the Plexiglas that the LED has to shine trough.

For maximum ease and customizability everything external is connected with connectors.


The MQ sensors are not all the same and needs to be calibrated. Put the sensor near fresh air or ideally outside and wait until the minimum value is reached. This is the value of clean air and you can change the values in the code accordingly. The code is filled with instruction to make it easy to understand where to change the settings.

Step 4: Assembly Part I

Picture of Assembly Part I

The assembly is split in to 2 parts because of to many pictures. Before you start the assembly make sure you have all the parts fabricated, painted and ready to go!

Assembly step 1: Fans

First you should build up the fan assembly with the 2 120mm fans, the wooden top piece, dual fan connector, fan to filter connector and the filter housing. Double check the direction of flow of the fans, they need to blow the air upward. 8 M4 40mm bolts is all you need and the bolts can be crewed direly in to the plastic.

Because 3D prints are never completely flat cause of material shrinkage you may need to tighten the bolts quite a bit, remaining gaps between the fans and the printed parts can be covered with tape.

Assembly step 2: lining up

The height of the wooden top piece on top of complete fan assembly is already set. All you need to do is align the bottom piece by putting in 3 ribs and check the angle of the ribs with the assembly tool. If you want to be sure you can put a couple more ribs in and check the whole shape but do NOT glue it all together just jet.

Assembly step 3: The ribs

Important is to leave at least 9 slot open where the sensor hole is located for easy installation of the electronics. And put the one special rib with the sensor cutout and the Plexiglas rib to the side for now.

Start off with 3 ribs in a triangular form like the previous step and triple check the alignment of the bottom piece and the angle of these 3 ribs with the assembly tool before touching any glue. I would recommend to temporarily secure these 3 ribs with tape and then start to work your way around, gluing ribs in place with wood glue.

Step 5: Assembly Part II

Picture of Assembly Part II

Assembly step 4: Electronics board.

The electronics board can be mounted in the holes already printed in the fan connector. If you want to you should use the smallest spacers that you can find because the tolerances with the ribs are pretty tight. PRO tip: if the holes in the electronics board won't align with the holes in the printed part, like what append to me.. Get a small screwdriver and a lighter, heat up the screwdriver until it's nice and hot, and then keep rotating the screwdriver while slowly pressing into the printed part. And voila a perfect hole to put a bolt in. keep in mind to not go completely trough the printed part, and you should use 10mm M3 bolts.

Assembly step 5: Finishing up

First let’s finish all the wiring. The fans can be connected and the power plug print can be glued in place after you welded the wires and connector on it. Now is the time to do a last final test to check if the complete system and all the electronics work. If all is well you can start gluing the last ribs in place. I would suggest starting by connecting the LED rib and putting it in place, next I should place the special wooden rib with the cutout for the sensor and the fan wires. Next up is put the remaining 7 ribs in place and BOOM. The main assembly is done!!

Step 6: The Filter

Picture of The Filter

After the assembly the filter housing can be unscrewed from the bottom of the OPEN AIR.

The trick with using 12v PC fans is to not restrict the air to much by making the filter to dense. Do not overdo it otherwise there would not be enough airflow to have a significant effect on the air quality.

The air will pass through 3 types of media designed to remove dust and toxins from the air

1. Fine dust filter

The fine dust filter on the outer side of the housing is the first filter the air encounters and it will remove dust particles from the air. These filters can usually be bought at large stores in the household sections.

2. Course activated carbon grid

Activated carbon comes in many shapes and forms and it can be a weird item to find. The simple solution is activated carbon for fish tanks! It's cheap, easy to find and it will work very well as an air purifier. So go to the nearest pet store or go online and search for the biggest grains of activated carbon. The larger the grain the better the airflow!

3. Activated carbon sponge

The Activated carbon sponge is also a product made for fish tanks that works great as an air filter medium. The best thing about these sponges is that they are nice and firm and thus can be used as cover, so the activated carbon grid won’t fall out the filter housing. Look for a square sponge at least 8 by 8 centimeters and cut is roughly round so it will fit snugly inside of the filter housing.

A good baseline is the layer design like I illustrated. But feel free to build up your own filter.


Picture of USE  >  IMPROVE  >  SHARE


Great job if you came this far and congratulations on your own OPEN AIR! I hope you did enjoy the build and that you learned some new things along the way.

The open air fits best in a small to medium room like office spaces, bed rooms and living rooms. I would say all the rooms up to a maximum of 35 square meters, otherwise it will be to must of a volume to clean on a constant basis. For use in big rooms the open air can be put on its side to blow a lovely breeze of fresh clean air toward you.

The OPEN AIR with the activated carbon filter will significantly improve the air quality and removes all unwanted odors and toxins from the air. However the activated carbon works like a sponge and will become saturated over time. Meaning that you should replace the activated carbon every once in a while, like every couple of months. Check step 5 for instructions on replacing the filter.


There are always improvements to be made and this project is no exception. Because the lack of skills and time I could not implement the following improvement:

PWM fan controlled by the gas sensor values.Small control panel for manual override buttons.Overall size of the electronics. Better sensor placement. NOCTUA NF-F12 fans.Different filter designs like: vertex dust chambers, UV sterilization, dehumidifiers, HEPA filers and more

If all goes well in the next time frame, I am going to test the effectiveness of this carbon filter versus a previous UV filter design. Result will be shared of course!


I really appreciate all the time and effort that you put in reading, making or improving this instructable! And I really hope you guys are now more aware of the problem of indoor air quality and that you are now a small part of the solution. So share this insturctable and your results and improvements. Together we can make a change!


Pfejou (author)2017-05-11

Hi ianvanmourik. Sorry if this question seems a little rhetoric to you, but im a adruino newbie. You said the sensor needs to be calibrated. i found the values that i assumed are the once to be changed. The question is how do i calibrate the sensor. i mean how do i get the CLEAN,DIRTY;GROSS values. thanks in advance

StevenVB made it! (author)2017-04-20

Hi Ian, I loved your build and took it as inspiration for one I made. As recommended in the comments I used a cylindric HEPA filter (only €10) and printed a funnel for the airflow. Tested the effectiveness with a PM sensor and it works!

Still need to find the time to write my instructable article :p

skilalowski (author)2016-11-29

what is the cost and time to make it?

Rusznic (author)2016-07-25

The design is very appealing though I would skip the arduino and sensor part completely and opt for constant filtration. More air can be moved this way and there is no way for sensor to detect all the types of gases and dust anyway.

Moreover from my experience with air filters (I worked in research institute researching military vehicle filters and gas-masks) using activated carbon in this application is kind of pointless. They get used up very quickly (less than a day) and literally soak up stuff from the air passively with water and humidity affecting them. You'll see them used in gas masks to filter out noxious gasses but the lifetime of those filters is about 2 hours!

A tubular HEPA filter or commercial paper filter would be a very good choice here. They have standard sizes and would fit very well inside this design. Such filters range from good to bad obviously but the best ones give great airflow with removing near all impurities from air (To qualify as HEPA by US government standards, an air filter must remove (from the air that passes through) 99.97% of particles that have a size of 0.3 um.)

DylanD581 (author)2016-07-05

Nice air filter! I don't have a need for the "purifying" function, so I may convert this awesome design into a fan! Cool case.

ianvanmourik (author)DylanD5812016-07-17

I will not argue with you, if you want to make it as a fan it’s ok! But anyone can make great use of some extra
clean air. And it is not even just about your own: “There are more molecules of air in a single breath of air than there are
breaths of air in Earth's entire atmosphere. Therefore, some molecules of air
you inhale passed through the lungs of Billy the Kid, Joan of Arc, Beethoven,
Socrates or any other historical person of your choosing.” - Neil deGrasse Tyson.

This quote was one of the greatest
inspirations for making the OPEN AIR, because we share the same air all over
the world. So make me and a lot more
people happy and make it a purifier :) thanks a lot for the complement tough!!

DylanD581 (author)ianvanmourik2016-07-17

You definitely have me convinced. Now what health benefits are there?

evandene made it! (author)2016-07-06

Maybe to consider using a standard filter element (5 micron and 300 CFM flow rate) including a Active Carbon foam pack strapped around it. (Standard on the market) See picture.

The standard filter element is hold in place against the little duct with a threaded rod and closed up with a wing nut.

I removed also the spacer 120x120 in between the fans because I have the experience that the air comes out the fan without turbulence. (with quality fans like you do suggest)

ianvanmourik (author)evandene2016-07-17

awesome work!! I really like the center bolt for the filter housing and the 5 micron and 300 CFM flow rate. I will
soon go on an adventure to find it for a good price because I have never seen
it before. You are correct about the quality fans, but I would still recommend using
a pacer. But the best way to find out if you really need it, is to just test
it. Thanks a lot for your input and good luck building your own. And remember
to show of your OPEN AIR when you are finished, I would make my day :)

Nighter3D (author)2016-07-05

May i give some input on the electronics?

Your use of a relay is rather crude and actually kind of unsafe. Microcontrollers are not meant to directly power a relay. small relays could (still not advised) but any larger and it starts to draw too much. Relays are always best to be driven with a Transistor acting as a switch for the coil. You could also just replace the entire relay by a Solid state relay or Power mosfet.

But what i really want to stress is that i don't see a Flyback Diode which is something i consider important. Magnetic coils like those in mechanical relays and fans store a bit of energy and when the supply suddenly stops (cause say a relay switches off) the magnetic field collapses resulting in a voltage spike that can be pretty high and pose a danger to other parts (like the controller). Flyback diodes accros the coils/fans can minimise the spike.

They may not look nescessary and your circuit more work perfectly fine atm, but when it comes to electronics it's better to be safe than sorry. Right now i'm not sure if the circuit can last really long.

nevyn.hira (author)2016-07-05

Hey this is pretty amazingly cool. Have you considered swapping the relays out for an optoisolator (the fans would be rated at around 250mA? In which case use a 2N222 in a darlington pair like arrangement with a PC817 should give you what you need.)? This would not only remove the clicking from the relays BUT also allow you to control the speed of the fans via PWM rather than a variable resistor. This would have a couple of implications:
* You'd use slightly less power i.e. you're not using power to heat in the variable resistor.
** You could use the variable resistor as a sensor instead to control the PWM if you really wanted it there.
* The code would need small changes as a consequence.
* You could have various levels based on the level of dirty air from the gas sensor eliminating the need for the variable resistor entirely. i.e. the speed of the fans would be based on the dirtiness of the air rather than preference.

Doc Cox (author)2016-07-04

Fascinating project, is there a need for the electronics or could similar device be made with just the fan, filters and a pwm, controller for fan speed, thank you for the inspiration regards Doc Cox,

LeslyG1 (author)2016-07-04


lfmlhy12345 (author)2016-07-04

cool!is a good idea!

evandene made it! (author)2016-07-04

Good idea and very useful now these days.

I would recommend to eliminate the pre-filter foam pack, the active carbon and the 3D printed carbon scrubber to be replace by a 5 micron pleated paper air filter cartridge with outer and inner reinforcement like a Solberg filter 30P. These kind of filters are mechanical self-supporting and with a flow rate of 300 SCFM it would be outperforming the original design many times. The 5 micron filter capability would justify eliminating the active carbon health wise but on the other hand it's adding functionality. the filter can be bolted on to a new to design FAN / base adapter. I made a little sketch and I hope I did contribute to this nice idea.$smthumb$

GiridharR (author)2016-07-03

Hi Mate,
Fantastic project. Using dust filters, it might get clogged over a period of time and cleaning too is not easy and the power required to push the air will go up considerably. Have you considered electrostatic dust filters? they dont obstruct the flow of air and can be cleaned easily. :)

ArifSae (author)GiridharR2016-07-03

agreed, replacement should be easy, but this article dosent recommend static either

mark_racal (author)2016-07-03


qiu_jason (author)2016-07-03

Looks very cool! thanks for your sharing.

KosmaE (author)2016-07-03

I would suggest adding a carbon monoxide sensor. Due to carbon monoxide poisoning being dangerous and becoming much more common. In addition to this, I would add IOT functionality. Given that the ESP8266 is so cheap, it seems like including it wouldn't hurt. Not only that, you would be able to monitor the environment of the room from anywhere in the world. Quite useful for people looking after the young or elderly.

ryanjohnlenz (author)KosmaE2016-07-03

Good idea, KosmaE, but just to point out the (semi) obvious.... keep in mind the filter wouldn't have any ability to filter out any significant amount of CO. If a CO sensor were incorporated, it would only be useful as an alarm (which would also need to be integrated into the design).

KosmaE (author)ryanjohnlenz2016-07-03

My intent was for it to be used as an alarm, both as an audible alarm and a push notification on the user's phone which notifies the user to ventilate the area. If CO levels get really high the system could send a notification to the user's neighbor. I know this sounds extreme. However, CO poisoning is potentially lethal. In my home city, A man used an indoor coal fire system with minimal ventilation. The result of high CO from the combustion of coal was detrimental. The man nearly died and ended up with severe brain damage. I agree that implementing this could be challenging but the assurance it provides is well worth it for many.

Maninthemoon (author)KosmaE2016-07-03

I would like to point out that carbon monoxide, if stirred up in a moving flow of regular air will dissipate, into x ppm, in no time flat, ... So why add something that will always give you "mixed results"? The open air concept is not a new idea, but there are different methods of achieving the same thing, ... A filtered fan always brings a fresh mix of air to any room, ...

When I was applying to be a general contractor, 1 of the questions on the test, was "What size fan, must you install into a washroom with no windows, or other air systems readily available?", keeping the reduction of odors/smells, in the forefront of my mind, & after spending a great deal of time researching the answer for this 1 question, I finally found the proper answer, ...

It was not the answer I had been xpecting to find either, but yes, there is a formula for this question, ...

behzad1970 (author)2016-07-03

Great concept, I like how you have designed it. It is clearly an amalgamation of three elements to my of, nature, art and technology. Good Job, Thanks.

jezzybear (author)2016-07-03

I love the aesthetic I think this would be great to combine with a lamp. I'm definitely going to have a go a making one

SidA2 (author)2016-07-03

wow, looks very cool

SidA2 (author)2016-07-03

wow, looks very cool

itisnot_me (author)2016-06-29

This is great. Serious questions:

1. Were you able to measure the dirty air going in vs the clean air out? Was there a major difference? (i did not see stats when I scanned the ible)

2. Is this powerful enough to offset the VOC's produced by the 3d printing, lasercut wood, electronics?

3. Do you suggest pushing or pulling the air?

I did draw up some designs to make one but have a chained horizontal array of fans that would use a standard store bought filter. But the issue is the size, fan pull/push speed, and activated charcoal sheets.

Maninthemoon (author)itisnot_me2016-07-03

great questions, they teach these concepts in underground coal mining courses, as well as including other gasses as well, ...

itisnot_me (author)Maninthemoon2016-07-03

Thanks. But seeing how we are starting an open source air purifier, yes its not the first but so far the most DIY and sexy, then we need to answer the important questions. Alot of the open source air purifiers that I found on here are either dead or you need some big machines to make the shell.

ArifSae (author)2016-07-03

box is awesome

johanmoberg (author)2016-07-01

Great design and well laid out instructable. Suggestions for improvement; 1. Remove both relays and use a single transistor with pwm from the arduino to change speed seamless. 2. Remove the vregs, you can input 12 v to the nano and use it´s own vreg to output 5 v. This should reduce the size of the board a lot + cheaper. Good job!

chrwei (author)johanmoberg2016-07-03

just keep in mind that at 12V input you can only get about 200mA out of the nano's regulator before it overheats and shuts down. if my math is right the MQ sensor needs about 150mA when heating, that doesn't really leave much for the LEDs and relay transistors and the atmega.

personally, I'd have gone with a little 1A buck converter. less parts, more power efficient, and room to spare for more sensors.

johanmoberg (author)chrwei2016-07-03

Well the 200 mA is for constant draw and very little airflow (only 1.4 W heat). I guess it's a matter of taste how you solve it, I'd say the best solution is to just read the sensor in 30 min intervals (+ life span of sensor). Then you´re about 60-100 mA average current plus it´s located next to the 120 mm fans.

TroyG1 (author)2016-07-03

this is a gorgeous project! love the radial laser cut design. As a less attractive but cheaper and functional, a box fan and furnace air filter which can be used in bigger rooms.

DougS2 (author)2016-07-03

why did you decide to use the MQ - 2 sensor? Isn't it a sensor for gas detection?

Akin Yildiz (author)2016-07-03

follow + fav + vote


HerbertD1 (author)2016-07-03

600m³/h is total BS for 120mm fans. 180 is max. 100 for "pressure optimized" fans.

deluges (author)2016-07-01

Beautiful design and great write-up that serve an amazing project perfectly.

Sverd Industries (author)2016-06-29

Well done, the led indicator panel was a really nice touch! Why did you choose to use two fans? Is there a great improvement in suction over using just one fan, and does this improvement scale to three fans as well?

Thanks! The filter restricts the air flow quite a lot. so you need enough static pressure to suck the air trough the filter. In this case using 2 fans does generate better air flow.(I did a lot of testing) Important is the 25mm spacer between the fans where the air has some time become less turbulent before it encounters the next fan. Putting more fans in series will only increase the static pressure, the maximum air flow will never be more than just one fan.

Interesting how you experimented with pressure and air flow. It's a well developed project!

2jdavey (author)2016-07-01

Do you have to buy premium to get the sizes of the parts or it available without.

Nick3085 (author)2016-06-29

Freaking awesome!

ethanpnorton (author)2016-06-28

This is amazing. Great documentation as well! Awesome work.

Rene Artois (author)2016-06-28

I have such carbon air purifier over my kitchen's burners. Though without arduino


Filters over 600 m3/h.

JulianAzz (author)2016-06-28

This looks amaizing too!

Herbsco (author)2016-06-28

Insanely well done, I am just getting into Arduino and 3D printing and seeing builds like this give me tremendous energy and excitement to be proficient in the technologies!

ForrestW (author)2016-06-28

This is awesome. Well done and not just a DIY project but a very sexy design for being an Instructable. I will definitely plan to build one of these, not just because I do need an air purifier but because this looks badass. If I do this one I think I am going to use same thickness aluminum or copper sheets for those blades.

ianvanmourik (author)ForrestW2016-06-28

Thanks for
the compliment I appreciate it! A metal
version would be really sick. Keep in mind the angle of the blades, but bending
metal gives a whole lot of other design options. Keep us posted if you decide
to make one.

Ps. everyone
could use an air purifier ;)

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