I have a circuit that I have for that but haven't tried yet.  It's for
measuring the airflow for my foundry casting furnace.  I'll PDF the
schematic tomorrow and post a link where you can find it.

An alternative, which was done in Circuit Cellar Inc a long time ago was
to use Ultrasonic transducers and measure the speed of the 40KHz ping
across sensors separated about 2'.

Bedtime in Victoria BC CANADA
Cheers,

John


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of marco genovesi
> Sent: Friday, April 05, 2002 1:20 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [EE]: Thermal anemometer sensor
>
>
> 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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