Re: embedded aviation computers.

[Brian Lloyd <brian@lloyd.com>]

On Fri, 11 Feb 2000, Jerome Kaidor wrote:

> *** I have a thought for a small embedded project:
> 
>   As it happens, I'm installing a GNS430 in my airplane.  Perusal of the
> '430 manual reveals that there is an input for OAT.  The '430 is already
> connected to the transponder bus, so it knows the pressure altitude.  With
> OAT input, it would also know density altitude.  In fact, one can read
> the density altitude off on a screen.
> 
>    There does not seem to be a dedicated pin for OAT input.  Rather, this
> information comes in as part of an ARINC serial data stream.

Right.  It is ARINC-429 data stream.  The problem with -429 is that it
doesn't support multiplexing of data so you need a dedicated port for each
device.  This has given rise to router boxes that transfer the data to
where it is wanted.  This is 1960's technology.

FYI, the Airbus and the new B-767 are using Ethernet for this kind of
data.

>   Sure would be cool if there was a pod with an OAT sensor and an ARINC
> output.  Unfortunately, we're talking airliner stuff here - the pod that
> does it is called an "air data computer", weighs a ton, and costs a king's
> ransom.  Now, we're talking about a job that could be accomplished handily
> by an 8751 hooked to an A/D.  Heck, the A/D could consist of a ladder
> network of resistors and a comparitor.  I bet even a PIC could do it.

This is the kind of stuff we are working on over on the avionics mailing
list.  The goal is to nail down the buss and the messages so that people
are free to do whatever implementation they want (use Linux as the OS for
your embedded system if you want) and yet still be compatible with what
the other guys are doing.

The kinds of things under discussion for development are:

* dedicated display/processor module(s)
* engine data collection module
* air data collection module
* various nav sensors

Brian Lloyd
brian@lloyd.com
+1.530.676.6513

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