FFP2 Mask Toaster

Description

As of this making, a SARS-CoV-2 pandemic creates an incentive to sterilize FFP2 masks for re-use. The temperature should stay around 80°C, but household appliances don't offer digital temperature readout or control, instead relying on bimetallic thermostat switches with about 10 K hysteresis.

A safe and scalable solution would be to use

* mass-produced and certified toaster ovens
* remote controlled mains sockets
* a simple microcontroller board with 433 MHz transmitter and thermocouple interface

mains-connected temperature controllers and industrial PID controllers are an order of magnitude more expensive and cannot be procured in sufficient quantities on short notice, while toaster ovens and remote controlled switches are ubiquitous and thus suited for situational response.

The core of this project will focus on describing and qualifying the proposed approach and on providing a cheap and simple microcontroller solution for its control.

Project Logs

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toasty waffles
helge • 01/22/2021 at 13:52 • 0 comments

Toasts

Initially, I saw this project by Vince float by on twitter which describes how to rework a sandwich toaster reflow oven. Useful, but currently I'm sure more people need to re-use their more expensive FFP2 masks. This build is close, but I'd like to turn it into something that's safe and that one can instruct other people to build without breaking certifications safety mechanisms that the appliances already come with. Preferably one would also want to use them again for their original purpose after the pandemic, creating no, or only a minimum of additional e-waste.

https://twitter.com/MicrochipMakes/status/13486757525569617

Temperature controllers

Industrial PID controllers that have temperature sensor inputs and relay outputs can be purchased for 15 to 500 €, which is outside the scope of this endeavor. Even if you come by them as surplus parts like the Jumo DICON ones below, they're not quite as handy. With them being intended for panel mounting, they may have exposed mains terminals at the back, and you wouldn't want to set up something like that with kids around.
On the other hand, current microcontrollers usually only lack the RF section to send commands to radio controlled mains switches which are usually sold in supermarkets in packs of 2 or 4. Temperature sensors can be NTC, PT100, PT1000, and with a little more effort (dedicated front-end chips or additional analog circuitry) also k-type thermocouples. So why not implement the temperature control in a microcontroller and send ON/ OFF commands by using one of the popular sub-1 GHz transceiver solutions. When in doubt, one can even repurpose the original remote control for the switch and make the microcontroller board emulate button presses.

I'm currently working on a little add-on PCB for OtterPill, Arduino Nano and compatible PCBs, but I feel that it's more important to get the idea out there and to get started than to finish the project before publishing it.
All I ask from you in return is to not buy all stock for some relevant ICs and leave me with 26 week lead times :D

Target Specifications

The German Paul Ehrlich Institute has published recommendations for FFP2 mask sanitizing for reuse. They comment on the bimetallic thermostat devices as insufficiently accurate and intend to update their recommendations when better methods are found.

80°C for 60 min was found to completely inactivate SARS-CoV-2 contamination. The Microcontroller board should preferably also provide the option to heat up to > 120-200°C to sterilize the device, killing off other pathogens so multiple people in a household can use one mask toaster.

If you found this helpful and get some results out of this project, please share your build. Thanks :)

https://www.fh-muenster.de/gesundheit/images/forschung/ffp2/01_ffp2_info11012021_doppelseiten.pdf