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Altitude encoder output voltages

 
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finn.lassen(at)verizon.ne
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PostPosted: Thu Jun 18, 2020 5:27 pm    Post subject: Altitude encoder output voltages Reply with quote
I want to make a serial to graycode converter to replace the AK350 for
input to Garmin GTX 320A transponder.

I'd rather have the altitude come from the Dynon D-10A than the AK350 --
no discrepancy between what ATC sees and what I see on the Dynon (at
29.92 alt setting).

I found the table on
http://www.aeroelectric.com/articles/Altitude_Encoding/modecascii.txt

I intend to use an Arduino Nano or similar.

But my memory is real vague on the polarity and voltage levels.

Is it correct that the encoder has open-collector outputs and the
transponder pull-up resistors to system voltage?

Does the transponder expect inverted inputs (0 in table no input and 1
in table pulling input to ground)?

Finn

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nuckolls.bob(at)aeroelect
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PostPosted: Fri Jun 19, 2020 6:33 am    Post subject: Altitude encoder output voltages Reply with quote
At 08:21 PM 6/18/2020, you wrote:
Quote:
--> AeroElectric-List message posted by: Finn Lassen <finn.lassen(at)verizon.net>

I want to make a serial to graycode converter to replace the AK350 for input to Garmin GTX 320A transponder.

I'd rather have the altitude come from the Dynon D-10A than the AK350 -- no discrepancy between what ATC sees and what I see on the Dynon (at 29.92 alt setting).

I found the table on http://www.aeroelectric.com/articles/Altitude_Encoding/modecascii.txt

I intend to use an Arduino Nano or similar.

But my memory is real vague on the polarity and voltage levels.

Is it correct that the encoder has open-collector outputs and the transponder pull-up resistors to system voltage?

Does the transponder expect inverted inputs (0 in table no input and 1 in table pulling input to ground)?

Finn

Man! That goes back to the dark ages . . . I did some
bench test sets for Cessna/ARC radios waayyy back when
wherein I think outputs from the encoder were
basically open collector with pull-ups in the load.
Hence, the "1" voltage was what ever the load
circuitry provided.

You can't go wrong with open collectors. Lay out
your board to allow adding pull-ups to a 5v rail
should they prove necessary/useful. If I'm all
wet and the polarities are reversed a simple
bit-flip statement will fix it.



Bob . . .

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cluros(at)gmail.com
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PostPosted: Fri Jun 19, 2020 6:53 am    Post subject: Altitude encoder output voltages Reply with quote
How much does an Arduino cost. For about $70 Dynon sells a serial to greycode converter.

On Fri, Jun 19, 2020, 07:38 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 08:21 PM 6/18/2020, you wrote:
Quote:
--> AeroElectric-List message posted by: Finn Lassen <finn.lassen(at)verizon.net (finn.lassen(at)verizon.net)>

I want to make a serial to graycode converter to replace the AK350 for input to Garmin GTX 320A transponder.

I'd rather have the altitude come from the Dynon D-10A than the AK350 -- no discrepancy between what ATC sees and what I see on the Dynon (at 29.92 alt setting).

I found the table on http://www.aeroelectric.com/articles/Altitude_Encoding/modecascii.txt

I intend to use an Arduino Nano or similar.

But my memory is real vague on the polarity and voltage levels.

Is it correct that the encoder has open-collector outputs and the transponder pull-up resistors to system voltage?

Does the transponder expect inverted inputs (0 in table no input and 1 in table pulling input to ground)?

Finn

   Man! That goes back to the dark ages . . . I did some
   bench test sets for Cessna/ARC radios waayyy back when
   wherein I think outputs from the encoder were
   basically open collector with pull-ups in the load.
   Hence, the "1" voltage was what ever the load
   circuitry provided.

   You can't go wrong with open collectors. Lay out
   your board to allow adding pull-ups to a 5v rail
   should they prove necessary/useful. If I'm all
   wet and the polarities are reversed a simple
   bit-flip statement will fix it.



  Bob . . .


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finn.lassen(at)verizon.ne
Guest
PostPosted: Fri Jun 19, 2020 11:45 am    Post subject: Altitude encoder output voltages Reply with quote
Half of the emails from the Matronics list server ends up AOL spam
filter. Several don't make it at all. Got this using the list browser:

"How much does an Arduino cost. For about $70 Dynon sells a serial to
greycode converter."

I ordered three Nanos for $6. May take some weeks to get them.
I have 74LS05 hex drivers and PC boards laying around.

Then there's the fun of DYI.
Then there's the fact that I can program it to accept any of the inputs
from the D-10A.
Not really needed, but there's plenty of space in a Nano for a table up
to 67,000' or higher.

Here's another question.
There are several serial altitude formats:

Format 1
Used By
Dynon Encoder Serial-to-Parallel Converter, Garmin AT (formerly UPS
Aviation Technologies)
Baud rate
1200
Format
#AL, space, +/-sign, five altitude bytes, T+25, checksum, carriage return
Example message
#AL +05200T+25D7[CR]

Format 2
Used By
Magellan
Baud rate
1200
Format
$MGL, +/- sign, five altitude digits, T+25, checksum, carriage return
Example message
$MGL+05200T+25E3[CR]

Format 3
Used By
Northstar, Garmin
Baud rate
2400
Format
ALT, space, five altitude bytes, carriage return
Example message
ALT 05200[CR]

Format 4
Used By
Garmin GTX330 (set on Icarus input), Garmin GTX327 (set on Icarus
input), Garmin GTX328, Icarus, Trimble
Baud rate
9600
Format
ALT, space, five altitude bytes, carriage return
Example message
ALT 05200[CR]

Format 3 and 4 apparently do not have an altitude +/- sign.
So, what happens when you're below 0' pressure altitude?
Gray codes go down to -1200'

Do they reason that if you're flying that low there's no radar coverage
anyway?

Finn

----------------------------------------------------------------------
I want to make a serial to graycode converter to replace the AK350 for
input to Garmin GTX 320A transponder.

I'd rather have the altitude come from the Dynon D-10A than the AK350 --
no discrepancy between what ATC sees and what I see on the Dynon (at
29.92 alt setting).

I found the table on
http://www.aeroelectric.com/articles/Altitude_Encoding/modecascii.txt

I intend to use an Arduino Nano or similar.

But my memory is real vague on the polarity and voltage levels.

Is it correct that the encoder has open-collector outputs and the
transponder pull-up resistors to system voltage?

Does the transponder expect inverted inputs (0 in table no input and 1
in table pulling input to ground)?

Finn

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