Introduction: Take Your Breath Away Mask DIY!!!
Wow! What a challenging topics masks are. I am not here to debate the philosophical or health issues so lets just look at the mechanical problem that they are supposed to solve and some of the problems they create.
Everything I have seen for why masks are recommended is to stop both doplets (Which are the large ones that fall onto surfaces quickly because of their size and weight) and microdroplets (you guessed it the small ones that stay suspended on air currents for a long time) from eventually contacting touchable surfaces or people directly. It is the microdroplets that have so many people concerned. They are light enough be be carried on air currents within a room allowing them to stay aloft and spread for several minutes.
Sharing is not always caring so what can we do to capture these droplets before we take them to the potluck of human experience?
Masks are designed to keep the water droplets that a person breaths, speaks, or coughs from entering general air circulation where they could come into contact with other people. The way that this has been done historically is to cover our microdroplet ports (nose and mouth) with something to catch the droplets before they escape. This has meant that people cover their nose or mouth with enough fabric that the droplets and microdroplets of water that are projected from a person's nose or mouth are caught in the fabric. This raises all sorts of questions about how effective different fabrics are at stopping these droplets and it has been interesting seeing the different research about which types are effective and very interesting to see that there are even fabrics that are counterproductive in that they make regular droplets into microdroplets increasing the hang time.
So that is what masks are supposed to accomplish but they also do so much more. One of their favorite things to do is fog up my glasses so in general it is nice to not wear a mask when I can. This is because I like to see people's faces which is easier if my glasses are not fogged up and also if their face is not also covered by a mask. The idea of having a mask that does not cover a person's face is not new. Looking through instructables I stumbled across some guides for masks that use clear mouth covers that are helpful for the deaf and hard of hearing that rely on lip reading to help understand people. Here is one of the great examples by aaronlaura04:
BUT!!! What if there was a way of stopping the droplets and microdroplets without having to wear a piece of material over your face? What if there was a solution that literally took your breath away and pulled the water from the air before it went into general circulation?
Well that is exactly what the Take Your Breath Away Mask is in this instructable.
Using a centrifugal fan to create a zone of negative air pressure (Think like a small vacuum) in front of my nose and mouth I am able to catch and collect the droplets and microdroplets that I breath out or that come out from speaking! Once the centrifugal fan catches these droplets it pushes them through a collection of desiccant beads to absorb the water. I have even found some that change from orange when they are dry to green when they are saturated because everyone knows that green means sick and that is what these beads are supposed to catch. The final result is a dry stream of air ejected downwards away from people rendering it safe.
However this would not be a very good infomercial introduction if I did not say, "BUT! That is not all... This has a whole host of benefits
- You can see the wearer's face!!!
- Reusable filter that is not touching your face. Easily rechargeable with heating which kills the virus.
- Breathing in is not restricted in anyway which makes it comfortable to use
- There is nothing pressing on your face or hanging from your ears to make them sore
- It will not muffle your voice!
- Your glasses will not fog up!
The goal is make this small, effective, and quiet so that a person can still clearly understand me.
Lets take a look at what parts are need to make this happen and then get down to it.
FTC Disclaimer: I earn a percentage of the sales through the affiliate links provided through Amazon.
If you click on the link it helps fund future projects but bear in mind it might not be the best price for this materials.
- Silica Desiccant Beads
- Battery (18650 Cell)
- Battery Holder
- Motor Driver
- Lazy Neck Phone Holder
- 3D Printer Filament
- MCU (MSP430FR5969 Launchpad)
- Super Glue
- Computer (3D modeling and C Programming)
- 3D Printer
- Soldering Iron
Step 1: Problem Statement
The problem statement is how to catch the air that is being exhaled from my mouth or at least what the air contains before it gets out into the wild.
This is a pretty broad problem statement since when I exhale there are a lot of different paths it can take. It can go out my mouth which projects outward or out of the my nose which projects downward. On top of this there is a wide power range that these particle can have from low velocity breathing to more forceful talking escalating much further into coughing or sneezing. A quick search suggests that a cough can be as high as 23 meters/second while a sneeze can be much higher at 46 meters/second.
This project splits the problem into two stages. First the air containing the droplets needs to be captured or corralled to keep it from getting into general circulation. Using a region of negative air pressure/partial vacuum in front of my nose and mouth should accomplish this for simple breathing and talking. Second the suspended water in the air needs to be stripped out. A desiccant that captures and holds water until it is removed through recharging will give and extremely high surface air means to capture the water in my breath.
The goal is to design a system that can catch the air and the droplets and push them into the desiccant. Since I do not want to have this project running at a level to stop a sneeze or a cough (I like to hear other people taking and I like it when people can hear what I say). I made a follow on project at the end that I call the Hurricane mask that is between 100 - 500 times more powerful to handle the sneezes.
Regardless of what you use either this project or a standard mask it still just good practice to cover your nose and mouth with with upper sleeve of a tissue of some sort when you cough or sneeze so functioning at these speeds will be a reach goal and not the primary focus.
Be advised this project is a demonstration of a concept and will likely not be acknowledged as a mask at any location.
So we need something that will create negative air pressure in front of my nose and mouth to draw the heavily particles to the desiccant and so for that we need a fan!
Step 2: Impeller Design
The idea behind the fan design uses one of my favorite types of fans. You may be wondering what is the deal with this RyanMake guy? He has a favorite type of fan? How odd!
Well now that we have that part of our relationship behind us let me dispel the suspense. I am a big fan of centrifugal fans. They have a lot of great qualities especially for this particular project.
- Efficient: Typically more efficient than a standard axial fan which is good since this will be battery powered
- Quiet: They can be quieter for the same amount of air flow than an axial fan. This is important because I will need to talk over the sound of the fan and people will need to hear me.
- Higher Pressure: They can push air harder through restricted spaces which is important because it will be pushing air into a confined space with desiccant which are obstructing the air flow.
With the pros out of the way there are a few cons. They are more complicated to make but lets put that behind us for now.
The first step was to open up TinkerCAD and decide on the general dimensions of the impeller. Since my TinkerCAD is configured in metric units my impelled is 50mm in diameter and 20mm in height.
I iterated through a few different designs to settle on a shrouded impeller that has backwards inclined blades (More on this in the next step). These were not the easiest to make since I ended up building them in about 1mm increments to get the full blade height. After that I tapered the blades to fit within the cones shaped shroud. The blades are further reinforced by using a series of stacked parabaoloids to create a tapered slope in the center of the impeller. This impeller is then shrouded to guide the air coming from the blades.
The progression for the build is documented in the pictures!
Now many centrifugal fans have the the air exist at a perpendicular axis from where it comes in but this design follows a different but still common path of having the impeller be inline so that the air flow does not change directions. The air enters in through the ~22mm inlet and then exits out of the ring at the bottom. Now on with what I promised about talking about the blades some more...
Step 3: Impeller Blade Design
This was a dark hole that I fell into a while but I was compelled to impel. What I came out the other side with is that I wanted backwards inclined blades. The reasons being that backwards inclined blades verses straight or forward inclined blades are more efficient, quieter, and capable of greater pressure which are very important factors for this project.
If you remember from the last step I talked about the blade a little bit and how I wanted a tapered backward sloping blade. Looking on places like Thingverse there are many accomplished models on there that have made some very beautiful blade designs and impellers. Right now I am in the very beginning of 3D modeling and TinkerCAD is an approachable and free tool so I thought I would start there.
The pictures show the modeling progression from a simple box that I then built upon with 1mmx1mm sections at various angles ensuring that the boxes overlaped to try and achieve the smoothest and strongest surface that I could with out gaps.
One of the benefits of 3D printing versus machining is the precision of the layers. What I mean by this is that 3D printing is more forgiving when it comes to the texture of surfaces. So while the pictures show a rather choppy blade this kinks and rough surfaces the 3D printing process bakes in a considerable amount of forgiveness.
Step 4: Motor Housing
This is what I am calling the bottom portion of the system where the motor is mounted and where the air is channeled through to the desiccant container that is attached to the bottom. This is also where the system connects to the neck harness.
I had to iterate through a few different motors to get a good balance between power, size, and cost and settled in a place that I had not expect and that is with the small hobby motors that you see everywhere on toys all over the place that look like someone stepped on them to squish them and give them two flat sides.
This had a small benefit that I had not expected at first and that the non-cylindrical shape will improve and simply the mounting. How can that be? Well with a perfectly round motor the surface contact between the mount and the motor had two jobs to do.
- Hold the motor in place to not fall out.
- Hold the motor in place to resist the force of the motor spinning the impeller.
By having the flat sides the second job is handled by geometry instead of friction.
This piece of the puzzle serves three other purposes.
- Place to mount the impeller cover over the impeller
- Mounting points to the neck harness
- Place to attach the desiccant cartridge
The process of design was a collection of making sure that other parts would play well with this part.
- Holding the motor body that is 15mm thick on the flat side and 20mm radius.
- Holding the desiccant can on the bottom using a slotted channel that mates well with the canister
- Connecting to the impeller shroud to protect the moving parts
- The GoPro-esq mount profile to connect with the neck holder. I will need to figure out how to use these to make other mounts for the GoPro
All told this was a complex part that took many iterations and clean up once the part was finished.
Step 5: Impeller Cover Design
The started out as the simplest part up feature creep snuck on in. Originally it was a small ring and then a cone cover over the impeller which would have finished this part by the second picture. However I wanted to add the option for an air guide that would improve the directionality of the inlet port to focus the negative pressure region in the area around my nose and mouth.
So what does this part do? Its purpose is to cover the impeller to protect it from being touched while it is moving. This was relatively easy since the dimensions where already defined by the impeller. I needed to follow a similar taper to the impeller but with enough space that it would not contact the impeller as it spun while not leaving too much space around the sides. I then decided to have this part overlap with the motor holder housings so that it would ensure that the air from the impeller went where I wanted it to.
I also wanted to have the option of having a inlet guide that is useful for concentrating and directing the negative air pressure region to be right in front of thee mouth and nose of the wearer. This was easy to accomplish by using the same slide in mounting channel that I am using for the desiccant hopper to all for interchangable inlet guides.
Step 6: Desiccant Catridges
This is a small container that I printed to connect to the bottom of the motor housing. Its purpose of to hold the silica desiccant beads that I am using and promote the air from the centrifugal fan to flow past them and then out a vent in the bottom of the container.
It is a simple canister that can be removed and placed in the microwave for easy recharging of the desiccant. It slides into a small channel in the bottom of the motor mount using the same slotted channel that I have on the impeller shroud in the previous step.
I had been thinking about using Molecular Sieves particularly 3A or 4A since they are much better at pulling water from the air and they also pulled CO2 which would be amusing to say that this device is trying to be closer to carbon neutral (I know it is no where near carbon neutral). The challenge with the molecular sieves are that they are harder to tell when they are saturated and they are much hard to recharge. The result is a I made a prototyping decision to use something that works even if it is not the end target of the design to not get blocked up on non-critical details.
Step 7: Motor Control
The motor control for this project is simple. Many motor control schemes use a full H-Bridge but that is because they want the motor to be able to both forward and backward. That is not a feature that I need for this project but it is much easier to find a pre-built H-Bridge and just run it in one direction..
The way a half-bridge works is by using something called pulse width modulation (PWM). What does that even mean? Lets take a control frequency of 10Khz (10,000 times per second). This control frequency is the number of pulses that occur each second and it determines how many times a second the motor speed can be adjusted. You may be wondering why would we ever need to be able to adjust the motor so many times a second? Honestly we do not need to adjust things that often but it is important to have a control frequency high enough so that the motor still runs smoothly.
So with this idea of a control frequency established what do we use to control it? Lets look back at the name of this method. Pulse, we talked about how the control frequency determined the number of pulses that would occur each second but the control comes from the term modulation. What does it mean to modulate something? Well if we are honest it means to change or control and in this case we are talking about the width of the pulse. If you send an continuing series of pulses that are 10% and 90% for each pulse you will being transferring just about 10% of the total available power to the motor from the power source. If we want more power then we can up the percentage of the pulse that is on to 50% or maybe even 90% or 100%. The motor serves as a collector of the electrical energy and outputs the average of the pulses as mechanical energy.
Using this controlled with a microcontroller to supply the control signals is the simplest way to achieve effective motor control for this project!
Using a little bit of code the microcontroller (MCU) can be used to increment of decrement the speed of the motor in the system by changing the PWM on time for the motor controller. The simple code attached handles this using a timer for the PWM and a little bit a debouncing for the buttons.
Using an MSP430FR5969 launch pad that I had sitting around in a box near my desk for the brains of the PWM for the Take Your Breath Away mask to feed into a DRV8833 motor driver IC the motor starts to spin. The MCU and the motor driver do not make that much of a difference in the project so if you end up making this project with other parts let me know!
The code is really straight forward using P1.2 for the PWM output since that is what the launchpad has it labeled for. Right now I am planning on tuning the motor speed as a hardcoded value in the code to keep the code as simple as possible. Speaking of which the code that I am using is attached.
The PWM output from P1.2 goes into AIN1 and BIN1 on the DRV8833 and the AOUT1 and BOUT1 go to the positive motor lead while the negative motor lead is connected to ground. I can do this because I only need the motor to spin in one direction so this simplifies the control scheme so that I do not have anti-phase PWM signals. I would say that this has the drawback of not being able to use the current protections of the DRV8833 since the current is not passing through the external sense resistors but after looking at the protoboard I see that there are no sense resistors connected and that the sense pins are floating or grounded so I guess I have no choice but to not use this feature.
There was a little bit of challenging wiring to be able to use a Li-Ion battery to make this project portable since the voltage range for powering the MCU directly has a max voltage of 3.6V so I am using the onboard regulator that drops the USB sourced voltage down but since the Li-Ion battery is not a 5V device I have to be careful to disconnect the battery whenever I am using USB power to program the board.
Step 8: Testing!!!
This was an interesting challenge. I had been thinking about how great it would be if it was cold enough to see my breathe. The reason being is that I could see just how effective it was at drawing in the small droplets that make a person's visible in cold conditions and I could also see if any of these visible droplets can be seen on the other side. I however do not have access to a walk in freezer and my wife did not want me emptying out a chest freezer so I could sit in it to test the project.
The result was a compromise of using a small, portable humidifier to simulate my breathing and talking conditions. The speed should be close to the same so it will be a great test for the impeller to see how well it create the desired negative pressure region and then it will be an incredible test for the desiccant beads because there is nobody alive that would breath out as much water as a humidifier.
How to test a sneeze or a cough? Well I have the industrial high-flow spray bottles that are for another project in the works that I think will work just perfectly.
Bare in mind these tests have the potential to be hazardous to the hardware since this will be much higher moisture levels and these motors are not water proof.
While these results are not perfect they are nothing to sneeze at.
Step 9: Insane Mode!
Now that the practical version has been tested and seen to work maybe you are more interested in effectiveness than comfort or practicality. Well do I have a version for you. This instructable ran out the design for the "Take Your Breathe Away" version of the mask but my wife had this great idea of one that could work under all conditions. I am calling this upgraded version the Hurricane Mask because it uses hurricane speed winds to accomplish the same thing as the smaller mask.
While the TYBA Mask which has no relationship with the frozen yogurt franchise uses an impeller with a 22mm inlet powered by a little motor consuming only a few watts of power. The Hurricane Mask is not messing around and takes every droplet prisoner using a 70mm ducted fan that consumes over 1000 watts of power. Outside of this difference and few changes to the parts and changing the motor control from an H-Bridge to an ESC control signal to accommodate the extra power the principle is the exact same.
I will not take long to re-gail you with the results. I think that that the video will speak for itself.
Step 10: Summary Thoughts
This project was a lot of fun. I learned a lot about 3D printing and I was able to get back into some of the electronics that I enjoy so much (yes, I know that this project was pretty electronics lite but I am working up to that).
I am looking forwarding to exploring this mask concept even further down the road. The potential to optimize the geometry and the motor selection to make this project even more effective and ultra-quiet.
This also opens up the door to a whole other host of other air quality issues out in the world outside of a pandemic that need to be addressed.
Another project that I am looking forward to doing next is taking a negative and turning it into a positive and by that I mean this mask project uses the principle of negative air pressure but my next project is revsiting the air umbrella which uses positive air pressure. So lets turn that fan and the frown from my cardboard attempt upside down.
Now I want to step back and talk about how important it is to see each other as people. There is a lot of heat about the mask debate and how things like this should be handled, but I urge you to see the good in others and seek ways to come together and build each other up instead of letting ourselves expand the divide. The best way that we can make it through hard times like this is if we value people as people and that we desire the best for individuals and the groups that they are part of.
Ok, well that might have seemed like blowing hot air but I hope you read the last paragraph and that it is sinking in.
Thanks for reading through my instructable and visiting my Youtube Channel RyanMake where I explore science and engineering ideas to see what sort of amazing potential is hidden just beneath the surface. If you would like to see more projects like this I would ask that you follow me here on instructables and like, comment, and subscribe to my youtube channel! Until next time happy making!!! RyanMake
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