Princeton Ventilator

They are apparently near mass production according to the PR - but that means it's all largely undocumented:

https://www.princeton.edu/news/2020/04/09/particle-physicists-design-simplified-ventilator-covid-19-patients?fbclid=IwAR1hpVxrwu1_jTnuuoTGz_k6MMVTlw8PwA_G10BhNvFn81ASXHnlbMoXmhQ

Don't know if they are really open source about it - so I will contact some of the authors.

PDF download: https://arxiv.org/abs/2003.10405