I’m building a lie detector based on heart rate, breath rate, and galvanic skin response. I have it all figured out except for breath rate. What sort of sensor should I use to detect breath?
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This makes me think of the automotive MAF (Mass Air Flow) sensor.
Essentially it is a small diameter resistive wire suspended in the air duct. A small current flows through the wire, and is warmed up that way. The wire resistance will change (due to the cooling effect) of air flowing over it. So at a specific regulated voltage, and used in a breathing tube, the current will change depending on breathing.
It could possibly even distinguish between breathing in, and out (due to assumption that air going in would be cooler than air going out).
You’ll need a strain gauge band to wrap around your subject’s chest and a detector that’ll take the (very small!) varying voltage generated by the strain gauge and turn it into something useful.