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Fighting Germs
Blog Pumping air in Covid lungs
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  • Author Author: cypresstwist
  • Date Created: 31 Mar 2020 11:49 AM Date Created
  • Views 1521 views
  • Likes 11 likes
  • Comments 9 comments
  • respirator
  • fightinggermsch
  • air pump
  • arduino
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Pumping air in Covid lungs

cypresstwist
cypresstwist
31 Mar 2020
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So I was trapped in my appartment as everyone else when all of a sudden I came to the realization that I had everything I neede to make a portable 5V respirator. The hospitals in Romania aren't yet crowded but they will be. And when that happens due to COVID-19 I know they will need respirators to keep people alive. It took me three to four hours to build this.

 

I had some drone standoffs made out of hard plastic that came to me by mistake with an eBay order a year ago. Thee are perfectly-shaped to hold an ovoid-shaped air pump. I also had enough acrylic sheets an screws to make an enclosure. Some DS04-NFC 360° Continous Rotation DC servo motors.

image

Using hot air I bent some transparent acrylic sheets to 90 degrees. These will be each attached to a servo motor.

image

One drone standoff was glued then better fied with screws to each L shaped acrylic plastic.

image

Then I made the transparent holdong platform out of thicker acrylic pieces I had laying around. Glued them with superglue then reinforced each base with 3M screws.

image

I scrwered-in each DS04-NFC servo to a 1cm thick plate after drilling holes in it.

image

I also made an enclosure for a 6V led/acid battery to make the respirator portable. The battery has a step-down tuned to 5V glued to it and cables with a jack connector attached. This way the whole platform can be carried away, moved or swithed to autonomous power in case of power failure. The autonomy should be of at leat two hours.

image

The logic is that each servomotor moves a white arm to the left and right, in sync. A manual, ovoidal air pump placed and secured in between these two will be thus constantly pressed and un-pressed depending on how I program the servos in terms of speed and pressure.

image

At first I wanted to use a micro:bit with a servo board add-on but the pulse of the servos was not correctly calculated and they wouldn't turn counter-clockwise.

image

So I've switched to using an Adruino UNO R3:

image

The Arduino can take 5V. The red, power servo wire goes to 5V, the black GND to GND in the Arduino, and the data connection goes to pin #3 and #4 respectively.

 

I am currently testing and tweaking the following code for the Arduino to control one of the servos:

 

#include <Servo.h> 
// testing with pin #3
int servoPin = 3; 
// we declare the first servo as Servo1 
Servo Servo1; 
void setup() {
// connect pin 3 
   Servo1.attach(servoPin);
// move the servo back and forth 
}
void loop(){ 
   // move to 0 degrees and waith for 0,7 seconds
   Servo1.write(0); 
   delay(700); 
   // move to 90 degrees and waith for 0,7 seconds
   Servo1.write(90); 
   delay(700); 
   // move to 180 degrees and waith for 0,7 seconds
   Servo1.write(180); 
   delay(700); 
   // move to 90 degrees and waith for 0,7 seconds
   Servo1.write(90); 
   delay(700); 
}

 

Reading the documentation on the DS04-NFC servo motors I've found out that a pulse width (Pw) ranging from 1000us to 1500us at 4.8/5.0V makes the servo motor move counterclockwise with a maximum of 45 RPM. As you move the value closer to 1500us the servo speed slows down until it reaches the 1500us value (corresponding to a full stop). A Pw of 1500-2000us moves the servo clockwise with the same speed, the maximum speed being reached at 2000us. The lower you go and get closer to 1500us, the slower it moves. You can use the same 1500us Pw to send a stop signal to the servo motor.


These servos have a 5.5kg pressure power each but their rotor cogs are made out of plastic. So I either superglue them and secure them with screws or use different servos I have around that have a metal rotor cog. Would not want these wearing down while in use.

 

image

(Will be back with more updates as I go along with the development. Yesterday left me dead tired and my house is a mess. Have to take a few hours time-off.)

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Top Comments

  • 14rhb
    14rhb over 5 years ago +4
    You are a genius - great work.
  • jw0752
    jw0752 over 5 years ago +4
    This is a great use of trapped at home time. Congratulations. John
  • Fred27
    Fred27 over 5 years ago +4
    You've done some impressive stuff, but ventilators are way more complicated than just an air pump. Even a simpler CPAP is complex. I found this was a very informative article on ventilators and why trying…
  • royce_jp
    royce_jp over 5 years ago

    I assume that we are going to use a BVM (Bag valve mask) aka Ambubag, for the actual ventilation

     

    This already has a valve for over pressure, and a oxygen inlet and reservoir.

     

    We will require an HMI that will allow the user to set the following parameters (this could be a 4 line alpha lcd with some keys or potentiometers):

     

    1. Breaths per minute (BPM). This will determine the interval between 2 compressions, Typically 6-10 secs.

     

    2. The intensity of a compression (aka Tidal Volume).

    This will determine the angle through which the motor moves (smaller angle = lower compression).

    This setting is needed for adult vs infant lungs etc.

    This could be calibrated with a pressure gauge (BVMs with pressure gauges inbuilt also exist) but in practice, adults typically need 500ml air per compression .. (Actually 7 ml x body mass in kg if there is time to calculate).

    It is easy of the volume of the bag is known - If using a 1000-mL volume bag, squeeze only halfway to obtain the correct tidal volume.

    In practice, you can adjust the setting to cause a bag compression just large enough to cause the chest to rise.

     

    3. Some kind of alarm to detect abnormal conditions like leakage, blockage etc.

     

    4. An advanced model might offer an option to route the air through a water bath at around 36*C (Temperature sensor/ADC required) to maintain humidity and temperature of the mucus inside the nasal area. However this is required ONLY in invasive ventilation where the nasal mucus is bypassed.

     

    5. Further advancement might be processing the exhaled air to avoid aerosoling of infection and filtration at the air inlet (not the Oxygen inlet).

    Both these will require modifications to the BVM.

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  • 14rhb
    14rhb over 5 years ago in reply to Fred27

    A great article thanks Fred. I had been reading about these for some time but couldn't understand how someone could breath out if air were being constantly pumped into them.

     

    Therefore I guess the air pump needs to be cycled from high speed to a lower tick over - and this could either be a pre-determined pattern or better still it senses the patients flow rate. I wonder if the same could be achieved using two different pressure supplies and a valve to switch between them?

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  • 14rhb
    14rhb over 5 years ago

    A simple and low-cost 'over pressure' device could be to T off the high-pressure supplied air and take via a tube 400mm below the surface of of a jar filled with water. As the pressure goes up the water in the tube would displace and excess pressure would release as bubbles from the tube. Lower max. pressure would be achieved by lowering the water level.

     

    I get this isn't perhaps a clinical solution but it could prevent lung damage.

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  • dubbie
    dubbie over 5 years ago in reply to Fred27

    Fred,

     

    The linked article was very interesting. I have had a bad chest infection in the past (as I assume have many people) which wasn't much fun, but what I remember was afterwards. For months, possibly years I 'felt' as if my breathing wasn't working. I knew I was breathing in and out but I would still feel that I wasn't getting enough 'oxygen'. The Doctor wasn't much use, either he thought I was making it up or he knew what the problem was and it would (should?) go away eventually - he didn't tell me anything.

     

    I decided to do something and tried deep breathing or conscious breathing, breathing in and out more deeply for short periods (long periods make you dizzy). I found that walking helped me to do this which is one of the reasons why I still walk, not too fast but just fast enough to get my breathing rate a little higher. I also found that the drier summer weather helped, as did retiring as I no longer drove an hour to work every day along polluted motorways. So gardening, walking and laying patios has worked for me (and being retired). Of course this could all just be total coincidence and my lungs would just have got better anyway.

     

    I have also found wine, lager and sleeping in the sun to be effective as well, but sometimes I think that might be wishful thinking.

     

    Dubbie

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  • Fred27
    Fred27 over 5 years ago

    You've done some impressive stuff, but ventilators are way more complicated than just an air pump. Even a simpler CPAP is complex. I found this was a very informative article on ventilators and why trying to build one may be dangerous.

    https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/

     

    I'm not trying to dampen your enthusiasm and I applaud your work, but please be very careful if you get as far as testing it on a person!

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