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In article <848@earvax.UUCP>, sbcd@earvax.UUCP (Scott Dynes) writes:
> I'm looking for help on the following: I would like to get/make an
> airspeed sensor for R/C models. This would require 1) a small
> accurate (and light!) pressure sensor that would run off a small set
> of batteries, and 2) a similarly small, light, low-power way to get
> the information down to earth. I'm thinking of having the output be
> a tone whose frequency is proportional to the airspeed. Does anyone
> know of such a system, or where to look for the individual pieces?

	As you are no doubt aware, airspeed requires differential
measurement (i.e., pitot tube), and therefore requires a differential
pressure transducer.  I'm afraid that I don't know about speeds of
model aircraft, but "big aircraft" will provide a pitot differential
pressure of 0.17 in-Hg (0.0835 psi) at 60 knots (the lowest airspeed
for which I know a value).
	A model aircraft application will require a small and lightweight
pressure transducer having some rather respectable sensitivity (as
comparared to most other pressure transducers) - so you will not have
much to choose from in an affordable price range.  However, it just so
happens that I have a catalog from SenSym (Sunnyvale, CA, 408/744-1500)
on my desk.  It appears that their P/N SCX01DN temperature compensated
monolithic transducer will do the trick, and it carries a small quantity
price of $ 49.50.
	You will have to provide a bridge-type signal conditioning
circuit since this transducer has a sensitivity of 18 mv/psi, and
you will have to exercise some care in circuit design to prevent
RFI/EMI from the engine magneto.
	For telemtry, the simplest method is through the use of
FM/FM telemetry; i.e., a V-F converter to modulate a transmitter,
and a F-V converter connected to an appropriate FM receiver.
	More exact circuit details would be difficult to provide over
the Net, but hopefully I have steered you in the right direction.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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