Re: embedded aviation computers.

["D.F.S." <dfs@xmission.com>]

> 
> *** 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.  
> 
>   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.
> 

Undoubtedly,

I listed some parts that could easily do this in one of my other posts.
Dallas Semi has some digital output temp sensors, and unless I'm mistaken
the Airinc 429 interface should be doable with differentail line drivers 
and uControllers.

It was not as simple as RS-232 serial data run thru RS-422 line drivers.
Oh well.

It runs at 2 speeds ~12.5 Khz and 100 Khz.

The ARINC spec is copyrighted, but these guys have an "Interpretation"
http://www.1553.com/

While you are at it, all with all the work of getting an arinc interface
tested and working, you could use a A/D to read both a Temp Sensor and 
Pressure sensor, and build a dedicated display.

Outside Air Temp.
Pressure Altitude.
Density Altitude.
Vertical Speed.
Altitude Alert.
Zulu Time.

Stick another pressure sensor out in the airflow and get

IAS & TAS as well.

There are atmospheric pressure transducers built for weather research
on the surplus market for ~$1.50.

BG Micro has LM34DZ Precision Temp sensors for $1.19.
They have 20 column by 2 row Backlight LCD display for $2.25.
Pics up to the task could be had for under 5 bucks.

Marc


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