** Updated** NEW DESIGN CHOICE

After discussion with Professor Yin and our client, we have decided to pivot and change the choice of air chamber of the system. We know are pursing a design that uses a bellows system as the main mechanism of holding the proper volume of air. We still will be using a linear actuator to move the bellows and instead of driving the system based on volume based feedback, it will be coded to run based on respiratory rates during resting/tidal breathing.

Through the prototyping process we have also developed a frame to hold both the bellows in place and to hold the actuator so that it can be connected to the bellows. We have also changed from using an Adafruit Microcontroller to using two Adruino Uno Microcontrollers. This was due to the Adafruit Micro-controller malfunctioning during prototyping and and the fact it is more feasible to run both the Actuator and Adafruit Pressure Sensor on individual boards.

Refer to photos of the New Design in the Final Product tab and/or the Design Sketches tab.

Bellows System

After comparing each of the individual components and choosing the highest scoring items, we were able to compile a final design based on these pieces in a fourth Pugh matrix. With 795 points, the design including a syringe using a linear actuator with a volume-based negative feedback system was the highest scoring of all the design options. This design scored highly on key specifications such as the ability to replicate lung mechanics and perform well over the course of many breathing cycles. By causing the linear actuator to respond to the amount of volume in the air chamber rather than moving on a timed pattern, the volumetric feedback system will ensure that the same amount of air enters and leaves the chamber. This system also allows us to measure differences in the amount of pressure in the air chamber with and without the NED during each breath cycle which is not possible with pressure-based feedback system as the beginning and final pressures would remain constant. Timing the actuator could lead to inconsistencies if the airflow through the system changes for each breath, but the target volumes will always be the same. While this design does not score as well on other features such as portability or evaluating irregular breathing patterns, we have decided these lower weighted specifications are less important for developing a minimum viable product.