<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 14 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>I bow to other peoples experience with these types of things, however, couldn’t a simple flexible vane switch (reed type switch) in the air flow detect which way the air is flowing and trigger an arduino to do exactly what you want depending on the direction of flow. The pressure in the line will change from the beginning of the breath to the end of the breath so a pressure switch would have to take that into account. If there is any flow in either direction the vane switch will work. No flow, and the lights could turn red indicating “the end”.<o:p></o:p></p><p class=MsoNormal>I am not familiar with the ventilator hardware, but it should be simple to extend the hose with your own insert with the switch built in. It is not being used in a life support function.<o:p></o:p></p><p class=MsoNormal>Good luck<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Bob Howard<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><a href="http://en.wikipedia.org/wiki/Sail_switch">http://en.wikipedia.org/wiki/Sail_switch</a><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>