#7 part
Building discharge poles
At the beginning of the outbreak, I was exploring options for the materials I could use in my prototypes. The parts could not be restricted or too expensive. One frustration came with the discharging brushes available on the market. They were effective, but they made with carbon fiber so they were expensive. Also, due to the heightened need for mask making machines, their price was about 50 times normal.
So I had to change my perspective. People working in the IC chip industry are very concerned about static as it could spoil the product. They use many ways to protect from a static charge. The material they use as a conductor is not as good as metal, but it draws out static charge continuously. We found the material to be much more affordable if you know how to hack them. You can find this material in the B.O.M. list of this instructable.
I made two discharge boards (one is black because I ran out of my white duct tape). Finally, I buried wire beneath them as connection.
Part 4: Building the hot air fan module
Why not use a hairdryer instead? In the beginning, experts did suggest that we should use hairdryers to sanitize masks. However, they also noticed people shouldn't use them for too long as it could damage the dryers. Also, a lot of people are not patient enough to hold a hairdryer for half an hour. Also, temperature control on hairdryers is not that accurate. Once it overheats, the air could melt disposal masks.
So we built this:
Custom designed air-heating unit
Heating such a big layer would take too much power. We chose a PTC heater like the kind you find in AC units. We combine it with a DC brush-less fan, which was quite powerful at 12V 0.6A.
We had two ways of controlling the temperature: One by soldering a thermostat switch on the PTC, another by using a DHT11 sensor to tell the MCU when to shut the heating unit down.
UVC treatment
UVC radiation kills bacteria and viruses. Many people know about this technology. The problem is that few people know the difference between UVA, UVB, and UVC. Some think that they are the same. That’s why there were fake UVC lights on the market when the outbreak began. In our project, we only trust UVC, unlike the kind of light that nail polishing machines use.
Here again, I faced some hard choices. We knew there were three ways to make UVC, the most common being hot cathode (HCFL), rarer is cold cathode (CCFL), and then there is UVC LED. For the environment and for shipping, it originally seemed that UVC LED was the best choice. But - we finally chose CCFL for many reasons. Like I have said before, we didn’t want parts that restricted or overpriced. A lot of research went into how we settled on CCFL.
CCFL driver board
CCFL tube
I installed two tubes in the box, one on the floor of the middle layer, and another on the ceiling. I stuck some wire clips to hold the tubes.
The cold cathode UVC tubes and driver board were low cost but still powerful. They run at 12V and consume 10 watts total power. A scientific paper said that 15 minutes UVC exposure to surfaces can kill almost all bacteria. We decided it was good to pair it with hot air.
P.S. The origin wire on the tubes were too short, so we need to cut and solder longer wires to extend them.
Washing function
You may ask, why wash the mask if it would clear all remain static charge?
Washing is optional. First, we don’t worry about the loss of static charge because we can recharge later. The main purpose of washing surgical masks or N95 respirators isn't to eliminating bacteria, it’s to remove the dust blocking the airflow. The static charge does not only sticks to viruses, but also tiny dust particulars. Hot air treatment can kill bacteria but it cannot remove the dust. Human sweat and fats also block the air, similar to how acne forms on faces. After reading the material properties of melt-blown, water was the best affordable choice. It can dissolve mineral salts and soluble stains and wash away insoluble particulars when the static charge is gone. More than just soaking though, you need water to flow. So I used a small submergeable pump and a short piece of plastic hose. I put a piece of adhesive double-sided tape on the pump to affix it to the wall of the water tank. I also extended the wires to be about 50cm longer.
Submergeable pump
If you want a better wash, I suggest putting a heater inside. This helps kill bacteria and dissolve stains. It would be a great help in cold countries. Remember to add a sensor or a thermostat switch to control the water temperature.
Other accessories
Plastic net to hold masks
You need two pieces of plastic net, listed in the material list, to hold the masks in place while they are being washed and blown. N95 respirators can be squashed to fit the net and without damaging them. You need some zip ties tied at one side to make a hinge so it can act as a net.
UVC exposure is harmful to humans so we need a door to block it. I came up with a simple solution. I cut a piece of PP hollow board that was 45 x 14cm. I drilled 4 holes, 4mm diameters each at 4 corners, and put 4 plastic rivets through them. The board can then be placed in between the gaps of the PC hollow board. Finally, I stick some velcro on two sides of the box and on the door to cover it. It looked rough but it worked. You can upgrade it with a hinge or reed switch with magnets to make it more secure like a microwave door.
I placed an OLED and 5 press buttons (four functions and one emergency reset) to the panel board. All buttons were soldered with XH2.54 2P wires. The OLED needed an XH2.54 4P doubles headed wire to connect.
