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


For the CHT and EGT sensors a thermocouple is pretty much required. They are
not overly expensive. If you get extension wire, you can weld the wires
together to create the junction. The problem with thermocouples is you need to
run the wire in one piece to the sensor or gauge. If regular wire is used you
introduce a cold junction that introduces an error. The extension wire is used
to run longer distances but you have to use matching connectors for the type
of thermocouple you are using. There is a number of different thermocouples
for different temps. Some are better at lower temps and some are for high
temps. If you choose to get adventurous, Write me as I have some that I saved.
Good for exhaust temps.
For the other temp sensors a silicone resistor can be used. They are cheap,
reliable and accurate when set up to read it, with a circuit board.  There was
the design in Kitplanes a while ago described by Jim Weir.

Dale Davies