Paul:
As a side-project for my HomeBrewedGlassPanel project, I am researching
and soon will be acquiring sensors to feed analog data to my DLP-IO20
data acquisition board.

I believe that the automotive sensors that I have experience with in the
past are all variable resistive devices of some sort. The internal
bellows-construction of most old pressure-sensors is obvious. And I
always had the impression that there was a little plunger on the end of
of some pressure sensors. I also suspect that temperature sensors were
nothing more than thermistors. These resistance-based sensors would all
be relatively high-current devices... something I would like to stay
away from.

I once did an engine-swap on a Ford and managed to get my wires crossed,
couldn't figure out at first why it took so long to get decent
oil-pressure, and why the engine temperature was normal immediately
after startup. :)

So I am breaking ground here in the digital world. I would like some
advice from the RotaryEngine bunch. Let's break down my search for
sensors into catagories ...

TEMPERATURE
There is no problem finding low-current analog temperature sensors for
use in the -50F to 250F temperature range, there are hundreds/thousands
of them available. The only problem I will have is finding one/some
inexpensive enough for my R&D budget that are bullet-proof enough for
the FWF environment of an aircraft.  I might land up boring a hole in a
bolt or brazing a plug into a pipe-fitting to make a socket that will
accept a cheapy sensor, then epoxy the device into the socket, leaving
some teflon-insulated leads exposed to the outside world.

I know these cheap sensors should work for water temperature and OAT,
but what about oil-temp, CHT, and perhaps even exhaust temp?  Platinum
thermocouples are a bit out of range of my R&D budget, I think.
I don't know how sensitive the A/D input is on the IO20 board, but I
suspect that thermocouple-based temperature sensors would require a
transistor or op-amp to give a usable signal. ???  Any suggestions.

PRESSURE
There are also quite a variety of pressure sensors available: classified
as gauge-pressure, absolute-pressure, and pressure differential.
It is interesting that some very inexpensive pressure differential
sensors are available, they are used as water-level sensors on
automatic-washers.  I should be able to find some of these and create my
own test version of air-speed and vsi indicators.  Somewhere in the last
month or two I saw a graph of pitot-tube air pressue (in H20") vs
airspeed... I've got to track that down again.  I'll probably have to
stick a pitot tube through the sun-roof of my wife's Subaru and go out
and break a few speed limits to test it.
Higher pressure/gauge-pressure sensors are more expensive, and perhaps
picking up the voltage-drop across a resistor in an high-current legacy
automotive oil-pressure sensor would be OK too.  Anyone know what latest
cars use for oil-pressure sensing?

ATTTITUDE
As you've discussed, there are solid-state gyroscopes, and solid-state
magnetic compasses available, and there are many solidstate sensors out
there that are used in these products.  However, most of these require
digital I/O, I believe.  And interfacing my GlassPanelDislay with
several digital signals will require more ports than are supplied on the
DLP-IO20 data acquisition-board. I will need to do more studying on
these issues.

So ... if anyone has any advice or experience with sensors, I am
listening.

R Berglund


I am away from my hanger, but check out National semiconductors LM-34 ( I
think) integrated circuit temperature sensor.

It is a three wire device +12, GND, and output.  It puts out a linear
voltage with temperature, and is good up to 300 F.



Bill Schertz
KIS Cruiser #4045
N343BS
Phase one testing Completed

http://www.national.com/mpf/LM/LM34.html#Overview

Dynon Avionics just issued their first newsletter today, 12/21/2011 and one
of the announcements is their change to solid state pressure sensors.  I am
guessing they did their research as so far the company has made many good
choices and are very customer driven.  Here is the link to  the web version
of the newsletter. It may help you not have to reinvent the wheel.


Chris Barber
Adding fuel to the very top of my tanks to make my final weight check for W&B