When [Unethical Info] was looking at air purifiers a while back, their eye fell on a Xiaomi 4 Pro, with a purchase quickly made. Fast-forward a while and suddenly the LCD on top of the device was showing a threatening ‘0% filter life remaining’ error message. This was traced back to an NFC (NTAG213) tag stuck to the filter inside the air purifier that had been keeping track of usage and was now apparently the reason why a still rather clean filter was forcibly being rejected. Rather than give into this demand, instead the NFC tag and its contents were explored for a way to convince it otherwise, inkjet cartridge DRM-style.
While in the process of reverse-engineering the system and doing some online research, a lucky break was caught in the form of earlier research by [Flamingo Tech] on the Xiaomi Air Purifier 3, who had obtained the password-generating algorithm used with the (password-locked) NFC tag, along with the target area of the filter’s NFC tag to change. Using the UID of the NFC tag, the password to unlock the NFC tag for writing was generated, which requires nothing more than installing e.g. ‘NFC Tools’ on an NFC-capable Android/iOS smartphone to obtain the tag’s UID and reset the usage count on the filter.
A password generating tool is provided with the [Unethical Info] article, and this approach works across a range of Xiaomi air purifiers, making it an easy fix for anyone who owns such a device but isn’t quite ready yet to shell out the big bucks for a fresh DRM-ed filter. This approach also saves one from buying more NFC tags, which was the case with the previous solution.
I don’t understand why the need to hack the nfc tag. You can reset the filter with a key combination.
I have a Pro H which has this NFC sticker on the filter, but it can be reset by opening the filter door (there is a swtich detecting that its open) while holding one of the capacitive button on the front (I don’t remember which one). It will display some diagnostics info on success. There was a nfc spoofer article here a few years ago for these, but again its kinda pointless if you can reset the filter via the air purifier itself.
Also don’t buy Xiaomi air purifiers. They drop support for it pretty fast once the new versio ncomes out, and you will not be able to get a new filter. The Pro H’s filter I have is rated for 18 months, but only after a year of the release of this version the filters are not manufactured and impossible to obtain anymore. The filters loose effectiveness over time, its a consumable item. So even if you reset them and the device stops complaining it won’t be as good as new.
This is ridiculous. I know it’s not attractive but building a Corsi-Rosenthal filter box is not only cheaper and DRM free but it’s also been tested to be more effective than most commercial units and is on the level of a HEPA filter.
Not attractive is probably the big issue there. Compared to the Xiaomi, that DIY filter box would not be wife-approved for many.
In it’s most basic form it’s an ugly monster, but with a bit of tinkering you can disguise it as a side table. Put the fan on the side and a solid plate of material on the top. Maybe put some loudspeaker cloth or other open fabric around the perimeter. What about putting some embroidery on the cloth?
For myself, I would be more tempted to make it in some kind of flat form factor. Something that makes it possible to hide it behind or even under a couch.
Pink spray paint exists.
That’s for when BigClive builds his version of this device.
Ehh… that idea is best as a quick option that uses what people already have, rather than a permanent plan that can’t be improved on by commercial devices or by a different DIY plan. Box fans aren’t the best type of fan for every job. It’s awfully easy to get a circumstance where a lot of air backflows around the blades instead of actually coming through the filter, and they can end up needing more power and making more noise than they should because they’re struggling with the pressure difference. That should be part of the reason for using a five sided box instead of just taping a filter to the grille, but it ties into filter selection.
Most furnace filters I’ve ever seen also aren’t anywhere near HEPA H13. They need to support an entire home’s HVAC, and that’s both a high flowrate and a situation where the existing ducts and grilles already produce a fair restriction so you want to keep the filter’s resistance low for efficiency. You have to tolerate a fair amount of particles passing straight through in order to get a low enough pressure drop at high flow rates through a limited area. I imagine to an extent, with the high flow rate you have multiple chances to catch the particle in the same time as the other filters only change that air once, but still.
https://www.iso-aire.com/blog/what-are-the-differences-between-a-merv-13-and-a-hepa-filter
For filtering a smaller amount of air to a high standard, axial computer/server fans actually can work, though only some are made for enough static pressure – the ones that are good when mounted onto heatsinks with a dense array of fins are reasonable options. Or centrifugal can work. The pitch of the fan noise may be higher / more annoying, of course, and you need to pick a means of speed control.
Squirrel cage (wheel) blowers are more effective with high grade filters than window fans in a square hole.
Here’s an idea. Get a 20″ box fan and a 20″x20″×4″ and a furnace filter. Tape the filter to the back of the fan. If the filter is Merv 12 or more, it will work to clean the air and work as a fan! Merv 15 is about where hospitals go to for cleaning the air. The replacement filters will be $30-$50. If the fan is on high for a while, they will last like a month or so.
During the Canadian Wildfires last summer, I used this to clean the air in the office I was in. It worked amazingly well. My allergies got better when in that room. Worse when I left. And the HVAC techs, who claimed it was pointless, were shocked by how dirty the filter would be, after a few weeks of use…. in non-wildfire times!
You can check if you need to replace it by buying a device that measures wind speed. No programing needed. Just a fan, a filter and some duck tape to keep the filter on the fan.
It’s an idea that’s been done and works, but there’s still a reason for other filters to exist, although not with DRM.
https://www.iso-aire.com/blog/what-are-the-differences-between-a-merv-13-and-a-hepa-filter
This has its own equivalence claims. Of course that’s per-pass, and the high flow rate gives many passes. I’d hope that it equates to catching the same particle next time if you miss it this time.
Box fans don’t love restriction; they backflow a bunch of air. That’s why a lot of people make a box out of filters, it lowers the restriction some. At least these are 4″, so there’s more surface area.
I went for cylinder-shaped densely pleated hepa filters that pack more surface area per volume, and have a circular output that’s almost perfect for a 120mm computer fan. Piece of wood to make a box with a hole in it, a few screws, it’s not as easy as duct taping two objects together but it’s not that bad.