I like to tinker. And I am a physician with a little knowledge of ventilators. If you have "it" and are in dire straights, you will need to be on a ventilator with a knowledgeable respiratory therapist running the machine; that will be in a hospital, and not something that can be cobbled together to work (the respiratory therapist).
On the other hand, just tipping the scale for survivability when a ventilator is not available, a simple "ambu bag," esp one that can have oxygen supplementation might carry the day. These are easily available with masks, hoses, oral airways. So I really like the idea posted above
https://web.mit.edu/2.75/projects/DMD_2010_Al_Husseini.pdf
But we can do it more simply. Use an inexpensive automatic BP cuff to inflate and deflate the ambu bag- wrap the cuff around the bag, you get the idea- get one with wall outlet option- and rewire the start button to a programmable momentary switch to control the start/stop timing.
Good luck to all of you, my friends.
Charles