Published April 29, 2020 © CC BY

COVID-19 Emergency Ventilator

Minimalistic Emergency ventilator with fine control over BPM, tidal volume and flow rate, with a digital interface.

IntermediateFull instructions provided8 hours24,570

Things used in this project

Hardware components

Arduino Nano R3

SparkFun Stepper motor driver board A4988

Stepper Motor, Bipolar

Alphanumeric LCD, 20 x 4

SparkFun Pushbutton switch 12mm

Resistor 10k ohm

Digilent 60W PCIe 12V 5A Power Supply

Ambu bag

Lead Screw 8mm

Software apps and online services

Arduino IDE

Story

Amid the global crisis caused by the corona virus pandemic, hospitals and healthcare facilities are reporting shortages of vital equipments. As makers it's our responsibility to combat the shortage by constructing makeshift-open-source substitute devices. Our country might be in a lock down but our ingenuity isn't !

One important device for which demand has ramped up is ventilators for patients who need assistance with their breathing due to the respiratory effects of COVID-19. Basically a ventilator is a machine that provides breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. A DIY ventilator may not be efficient as that of a medical grade ventilator but it can act as a good substitute if it has control over the following key parameters

Tidal volume: It's the volume of air delivered to the lungs with each breath by the ventilator - typically 500ml at rest.
BPM(Breaths per minute): This is the set rate for delivering breaths.
Inspiratory:Expiratory ratio (IE Ratio): refers to the ratio of inspiratory time:expiratory time.
Flow rate: is the maximum flow at which a set tidal volume breath is delivered by the ventilator
Peep (Positive end expiratory pressure): It is the pressure in the lungs above atmospheric pressure that exists at the end of expiration.

refer this link for more information on ventilation parameters https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6212352/

My design is based on the automation of the manual BVM (Ambu-bag),which you can find in any medical supply store. It is a hand-held device commonly used to provide positive pressure ventilation.

When the bag is squeezed, the air enters the lungs of the patient, while the nonreversible breathing valve prevents backfiring of the exhaled air. Then the AMBU bag self-dispenses by sucking air from the valve from its back side. Either ambient air can be used as "fuel", or an oxygen cylinder can be connected. In the latter case, it is possible to connect a tank to collect excess oxygen, which was not used by the patient.

Most of the DIY ventilator out there are based on ambu bags and a direct drive actuator. In my design, I've tried to simplify the actuator mechanism and I also made a better user interface for the unit.

conceptual design of emergency ventilator mark1

The key element in my design is a linear actuator which is coupled with a lever mechanism that can compresses the ambu bag. A control panel is also provided for precisely controlling the ventilation parameters.

Use plywood or similar sturdy materials for making the housing and the lever mechanism. Make a cut under the lever arm so that the ambu bag can rest there without sliding. I am not suggesting you any particular hardware (nuts, bearings,..etc) because you may have a hard time in finding parts in this adverse situation. But make sure you follow the design. For those who own a CNC, I'll try to upload plans soon.

Actuation Mechanism

In order to make a linear actuator, I used a bipolar stepper motor integrated with a lead screw(or a Nema 17+coupling) and coupled it with a traveling nut. As the shaft of the motor rotates the traveling nut translates along the screw so that linear motion is achieved.

In the end, control over ventilation parameters can be achieved by varying;

No. of rotations (stroke) ----> Tidal volume
Speed of rotation----->Flow rate
Steps in clockwise : steps in anti-clockwise direction--->IE Ratio
Frequency of direction change per minute---->BPM

Circuit

I'm using an A4988 for controlling the stepper motor. The A4988 is a microstepping driver for controlling bipolar stepper motors which has built-in translator for easy operation. This means that we can control the stepper motor with just 2 pins from Arduino, ie one for controlling the direction of rotation and the other for controlling the steps.

For user interface I've made a control panel out of a 20X4 character display and 3 buttons (for up, down & ok functions). You could simply connect the display directly with arduino but I'd prefer using an I2c display adapter so that you can plug and play without a mess. 10K resistors are added for each individual buttons for pull down purpose.

Wire the components as shown in the diagram. Make sure that you had installed all the necessary libraries mentioned in code. Now, upload any of the sketches provided to your arduino. Use a 12v SMPS (3A min.) for powering the setup.

On running the test code, the motor executes cycles of clockwise& anti-clockwise rotations so that you can make sure that the actuator is running smoothly.

For testing the control panel and the device as a whole, upload the final_code.ino to the arduino. Now you can interface with the ventilator via control panel. By default, all the ventilation parameters are displayed on the screen. Use 'up'/'down' buttons to switch between parameters and press 'ok' button for selecting a parameter. Again use the up/down buttons to increase/decrease the value of the selected parameter. Finally press 'ok' to confirm the value.

Default Screen

Assemble the circuitry and the power supply unit inside the ventilator housing and make sure everything is fixed in place.

I had trouble finding resources for making the housing for mechanical parts. So I had to use what's available. But as you can see I had followed key features in my conceptual design while building this version and it works way better than I expected!

emergency ventilator_mark1

Feel free to ping me for any queries related to this project. Stay healthy, stay safe!

test code

#define EN        8  
#define X_DIR     2 //Direction pin
#define X_STP     3 //Step pin

int delayTime=30; //Delay between each pause in uS
int stps=6400;// Steps to move

void step(boolean dir, byte dirPin, byte stepperPin, int steps)

{
  digitalWrite(dirPin, dir);
  delay(100);
  for (int i = 0; i < steps; i++) {
    digitalWrite(stepperPin, HIGH);
    delayMicroseconds(delayTime); 
    digitalWrite(stepperPin, LOW);
    delayMicroseconds(delayTime); 
  }
}

void setup(){
  pinMode(X_DIR, OUTPUT); pinMode(X_STP, OUTPUT);
  pinMode(EN, OUTPUT);
  digitalWrite(EN, LOW);
}

void loop(){

  step(false, X_DIR, X_STP, stps); //X, Clockwise
  delay(100);
  step(true, X_DIR, X_STP, stps); //X, Counterclockwise
  delay(100);
}

Credits

ANUVIND ASOK

2 projects • 42 followers

I'm an Artist, Innovator and Engineer by profession specialized in robotics, computer vision and automation.

COVID-19 Emergency Ventilator

Things used in this project

Hardware components

Software apps and online services

Story

Actuation Mechanism

Circuit

Code

test code

Git repo

Credits

ANUVIND ASOK

Comments

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COVID-19 Emergency Ventilator

COVID-19 Emergency Ventilator

Things used in this project

Hardware components

Software apps and online services

Story

Actuation Mechanism

Circuit

Code

test code

Git repo

Credits

ANUVIND ASOK

Comments

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