I have to monitor wind flow from a cave entrance. Air flow (in-out) is
usually fast in Winter & Summer (10-30 ft/sec) but is often very "light" in
Spring & Autumn (less than 3 ft/sec) and probably a "cup" anemometer isn't a
good choice for this low values, so I'm thinking to a kind of "thermal
anemometer" circuit (not necessary an "hot-wire" type), simple to build and
not too expensive in power requirements (max. 1W) and in accuracy (+/- 10%
accuracy)

I want use my 16F84 logger to do this job, so the simplest way that I know
is to measure a frequency with TMR0 (I already have a TMR0 routine to read a
conductivity sensor).
The "ideal circuit" that I dream is a kind of "overheating" sensor (a
thermistor?) that outputs a frequency, or that I can easily convert in a
freq. I have searched on the web a sample circuit, but at the moment I
haven't found anithing (enough simple..).

Have anyone any suggestion for build this circuit?

Thanks in advance
Marco

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