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From: tswift@well.UUCP (Theodore John Swift)
Newsgroups: sci.electronics,rec.models.rc,rec.aviation
Subject: Re: Electronic variometer plans wanted
Message-ID: <13654@well.UUCP>
Date: 15 Sep 89 18:59:46 GMT
References: <25730@iuvax.cs.indiana.edu>
Reply-To: tswift@well.UUCP (Theodore John Swift)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 49


VoW^?{

>I need references and construction details for electronic vertical-
>speed indicators (called variometers by sailplane pilots).  I'm told 
>that plans have been published in magazines of soaring and remote-
>control aviation.

Frank;

Yes, there was a variometer construction article in the March 1969
"Flying Models" magazine by Maynard Hill and R. Ben Givens.  They used
tiny (~.005" dia.) bead thermistors placed across the center of a 1/16"
diameter tube.  One bead is immediately "downstream" from the other, almost
touching, so air blowing either way will create an imbalance in the bridge
circuit, giving you magnitude and direction of flow.  Maynard Hill and
a bunch of his friends keep popping up in the literature with things like
this, and with electrostatic autopilots for RC aircraft; they all work(ed)
for Johns Hopkins Applied Physics Lab and got *paid* to develop these things!
  If you're also interested in the electrostatic goodies, write to
  Aeroprobe Technology Corp.
  2001 Norvale Road
  Silver Spring, MD 20906
Mr. Hill & Co. have developed an autopilot "kit"

  There's a "Solid State Barometer" construction article in the June 1984
issue of Radio Electronics, p. 41, which uses a SenSym pressure transducer.
You may get some ideas from this, but medium- and long-term drifts may be
a problem.
  There's an article on the fine points of thermistors: "Practical Design
Techniques Tame Thermistor Nonlinearities" in ._Electronic Design
 News_ (EDN),
20 Jan 1983.  Copies of these articles are in the mail.

For your cave measurements, you probably don't need the radio downlink, or
you could take the bridge output and use it to drive a voltage-to-frequency
(V/F) conve.rter for longer c
able runs.  An LM 555 would
 work;
 various other
specialized chips, such as the LM 566 VCO would also work.

How do you plan to measure the flow in and out of the cave?  Seems to me
you'd have to block off the entrance and insert your flow sensor through
the barrier.
-- 
Ted Swift                        "Mortui vivos docent"
{hplabs,lll-crg/lcc, pacbell}        The dead teach the living.
               !well!tswift