Thanks Glen, that looks very interesting. But I'm afraid that this is
going to turn into a Project instead of something I could just sling
together over a weekend. Still... Very appealing.
Where would you suggest I start looking? Googling "breathing sensors"
got me all kinds of unrelated stuff.
"respiration rate sensor" seems to be a slightly better search term,
although I had no luck finding an example of a pressure based sensor with
that search term. Some of these place a tube in front of the nose and
mouth to sense stagnation pressuure (similar to a pitot tube); I think
that these are the most accurate type available.
The sensors used in sleep studies often use thermistors (never hot wire),
which as someone else mentioned have better sensitivity than the hot wire
type, and much better snot resistance. The main problem with these is
that you inhale ambient temperature air and exhale body temperature air,
which provides a much larger thermal signal than the airflow cooling of a
heated thermistor, so it is difficult to get an accurate flow
measurement, although they are very good for inhale/exhale timing and
thus good at detecting apnea. For this purpose a single unheated
thermistor is adequate.
I just tried "pressure based breathing rate sensor" as a search term and
got some interesting results, including:
<
http://www.pasco.com/prodCatalog/PS/PS-2187_pasport-breath-rate-sensor/>
More expensive than the (presumably thermistor based) sensor from cooking-
hacks, and even a plain differential pressure sensor from digi-key is
over $100, although there are undoubtedly cheaper pressure sensors of
suitable sensitivity (a few cm H2O) available somewhere.
I like the idea of hacking your CPAP for a usable signal as a low cost
alternative, although that does limit your measurements to while you are
using the machine.
You might ask the doctor who did your sleep studies for sensor
recommendations.
As I mentioned before, I've already had two comprehensive (everything -
EEG, EKG, breathing, effort, etc) sleep studies that had so many wires
hanging off me I was amazed I could go to sleep at all
Now I have
this one specific little measurement that I want to do. If my debit
card doesn't burn a hole in my pocket and I am forced to go your
suggested route
then I think the hot wire anemometer is going to be
the solution.
Thanks again for your suggestion.
John
You're welcome, and good luck with your project.
Glen
