UVC is a germicidal wavelength of the UV spectrum. With sufficient intensity, UVC can deactivate viruses in air as fast as you can breathe.

The goal of this mask is to provide a way for people to protect themselves from COVID while allowing for expressive social interactions. The design aims to create easy breathing with a fan that keeps fresh air available in the mask, while also regulating airflow speed so a single UVC LED can disinfect air. An aluminum tube internally reflects UVC as air travels through.

I am designing a mask for production, and have made this as one of the prototypes. Since there will not be any UVC masks on the market for months, I thought I would share this as a temporary solution, or just as a quarantine project for DIYers. It uses all standard parts.

Open to any feedback about the design. Stay safe everyone!

Step 1: Materials and Tools

Tools:

Soldering Iron
3D printer
Vacuum forming machine (<$100 on ebay)
Multimeter

Materials:

Step 2: Print Enclosure

Find the .STL files for the enclosure at:

https://github.com/jackmqiu/mixellatormask

There is a top shell, bottom shell, and 2 chamber caps. The Solidworks part files are available as well for your own adjustments!

Using standard slicing in Cura makes this about a 4hr print.

Step 3: Cut and Bend Aluminum Tube

I popped the fan in first to check that the print dimensions are correct. Then I cut the aluminum tube.

I cut out a longer length than I needed, about 10", so I could have some leverage while I bent the tube. 6" is enough for air to disinfect as it travels through the tube at 10 liters a minute, the higher end of normal human air intake rate. The U-bend with straight sections entering air intake and exit chambers should be just over 6".

Make sure that the tube can enter both chambers while siting in the enclosure grooves, then mark and cut.

Step 4: Electronics Pt1

Solder battery leads onto the B+ and B- pins of the 18650 chip, wires going out the bottom of the chip
Glue switch into socket, solder 18650 chip's OUT+ lead to first 2 pins of switch
Solder 18650 chip's OUT- lead to IN- lead of voltage converter chip
Pop in 18650 chip into it's spot in lower right corner of the enclosure top shell face down. You should be able to see the micro USB port through the opening of the enclosure
Place Arduino nano into position at top of enclosure face down as well. Check that the micro usb port is lined up with the groove on the side

Step 5: Electronics Pt2

Move voltage converter chip into its spot over the 18650 chip. Solder the 3rd lead of the switch onto the IN+ lead of the voltage converter
Hook multimeter to OUT+ and IN+ of voltage converter, and use screwdriver to adjust the voltage output to 12V

Step 6: Electronics Pt3

Solder wires to Vin and GND leads of Arduino Nano. Use the GND next to Vin. The wires should reach OUT+ and OUT- of the voltage converter
Solder the negative lead of the fan to middle pin of your C1815 NPN transistor
Solder emitter pin to GND and base pin to D2 lead of Arduino. You can search for the transistor to see which pin is which
Solder GND wire from Arduino that you attached earlier onto OUT- of voltage converter
Solder the Vin wire from Arduino and positive lead of fan onto OUT+ of voltage converter

Step 7: Test Fan and Connections Up to This Point

Plug Arduino in and upload Arduino sketch from:

https://github.com/jackmqiu/mixellatormask/blob/ma...

Unplug Arduino and plug micro usb into 18650 chip. You should see the chip light up red, indication the battery is charging. Toggle the switch and the fan should also turn on. The 18650 chip should provide power while battery is charging

Feel welcome to update the sketch! This setup allows you to change the speed of the fan by updating the PWM output value. According to the datasheet this fan is able to output more air than you need, but with the narrow tube and light filter as resistance, I just have it set to max.

Step 8: Affix Aluminum Tube

use black fabric to close off exit end of tube -our goal is to block UV exiting the tube while allowing airflow
Add sealant to bottom of tube junctions and press down tube

Step 9: Affix UVC LED and Close Off Intake and Exit Chambers

Add solder to anode and cathode of LED
Glue onto raised tab on the enclosure
Solder wires onto LED
Solder 50 Ohm resistor to anode and solder resistor to OUT+ of voltage converter
Solder cathode wire to GND of Arduino
Optional: power Adafruit UV sensor and test UVC intensity - look at the datasheet to convert voltage reading into radiant intensity. Make sure to wear gloves and cover skin/protect eyes
Add sealant and affix both chamber caps

Step 10: Make Mask

Form mask shape out of clay - make sure shape fits vacuum machine
Allow clay to dry
Load some bbs (come with vacuum machine) and your mask mold. Load plastic sheet
Turn on heat on vacuum machine, wait until plastic sheet sags 1cm before pulling lever and flipping vacuum switch for a few seconds. Turn off heat immediately and allow mask to cool.
Don't step away from Vacuum machine while heating even though it takes a few minutes. The plastic sheet can catch on fire if overheated
Cut around edge of mask until you have a comfortable fit, making sure to leave some of the flat section on the edge for straps
Cut a hole and pop on a valve
Cut 2 slits on each side and weave strap through as pictured