Mauricio,

All of the approaches you listed have been tried as well as a few more. 
But first off, do you really want "air speed" or "mass flow rate"?

One method to measure flow rate is a resistor (just like current). A 
tube with some sort of restriction is used with differential pressure 
sensing.  The delta-p is related to the flow rate although it is 
nonlinear.  Pressures developed are generally very low.

Google on spirometry, spirometers, pneumotach, etc. Good luck!

Mauricio Jancic wrote:
> I want to make a alcohol breath analyzer, how can one measure the air speed
> when blowing trough the analyzer's tube?
> 
> -          I could do it with a small encoder and a propeller (I don't know
> for sure if that's the English word.)
> 
> -          I can do it with a Pitot tube, but I think its intended for 0.3
> Match and above speeds. it that correct? 
> 
> -          The Venturi tube its intended for non compressible fluids
> 
> -          What about a couple of ultrasonic transducers and measuring the
> propagation delay?
> 
> -          Hot wire? .. Nahhh.
> 
>  
> 
> Any other suggestion? Best approaches?
> 

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