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Transponder Serial Connection Question

jrvssgl

Well Known Member
I was wondering if anyone could lead me straight on wiring an altitude encoder to a transponder via serial connection using Icarus altitude. I am trying to get my Odyssee from MGL wired to a Garmin 327 transponder and thought I wired it right, but it will not display FL or Altitude information on the transponder. I have only the tx on the Odyssee hooked to the RX on the transponder as well as it is grounded and shielded. The only thing I can think that might not be right is that the tx on the transponder should be connected to the rx on the MGL as well? Thanks for any and all help.
 
Hi Jarvis -

I just installed a 327 hooked up to Dynon, and it sounds like you have it wired correctly - you should only need the one-way communication. Have you done the "setup" steps on the transponder to let it know it should be looking for Icarus data on the serial line? And I assume there is a similar setup step on the MGL? First things I'd check.

Paul
 
Still no worky

Yes, both the MGL is Set for Icarus ALt, so is the 327 set to Icarus alt on ser port 1. It will not communicate. Is there any way to troubleshoot either device?
 
Remember the GTX327 has TWO Rx lines. One is for altitude information and the other is for Aviation data used to switch automatically from STBY to ALT. The serial port for altitude is pin 19. The serial port for Aviation data is pin 2. Make sure you have the MGL connected to pint 19 for altitude.
 
Yes it is wired to pin 19 and enabled in 232 port 1 for Icarus. All other ports are disabled. I pulled the harness and verified all wiring is correct. Hmmm........ \My new plan of attack is to wire it using grey code. After talking to Matt at MGL who has been a great help for all questions that have been fired his way, has offered to send a me a free company made harness using grey code. Thanks to Matt and everyone here who has tried to help. Definetly a mind puzzler. Just hope it isn't a component problem.
 
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Does the MGL have a way to see if the serial port is actually putting out data (like the GRT guys do - like a comm port inspector or counter or datastream monitor)? Can you change the baud rates from the MGL? They do need to match.

There should be no reason to go through all the wires and hassle using grey code if your EFIS is outputing data. It's ONE wire, which is far superior to running a dozen of them to get the same thing. Sort of a bandaid that doesn't really fix the issue. The issue is simple - either the MGL isn't ouputting air data, or if it is it's at the wrong baud rate. Lastly your TXPDR could be bad (not probable if it's new, but possible). 99% of the time we see issues with serial data, it's the data coming from the EFIS or the baud rate of said data.

Cheers,
Stein
 
Stein

Thanks for the advice. I can not find any such way to change baud rate with the Odyssee or even see what the baud rate is. Matt did state that it has worked with other installations using the same equipment so it really should work in this instance. I wish i had access to a data stream monitor to make sure but I don't. The Transponder was purchased brand new, so i am going to fly to the city as soon as time alows and get them to plug the transponder into there equipment to make double sure that it is not a problem with that component, just too narrow down the source of this problem. And yes I agree the serial connection is the connection of choice as it is supposed to be a little simpler. thanks again Stein
 
One thing to check with the GTX-327: When you make a configuration change, it's not saved until you move to the next step (I think it's the Next button).

I made this mistake a few times, changed the config, then exited setup. If you do that, the config won't stick.

Vern
 
Okay, does anyone know what Baud rate the 327 accepts. I believe that the MGL is at 9600. Garmin does not have this in the installation manual unless I just can't see it. And what does Icarus mean exactly?
 
Jarvis,

I just reviewed all of my documentation for my 327 and EFIS, and nothing says what the baud rate needs to be! So.....I just went out to the hangarr and powered up the system to read the configuration page - my GRT EFIS sends the altitude data to the 327 at 9600 Baud.

The Garmin 430 Install manual shows the Icarus format to be:

ALT<sp>12345<CR>

where:

ALT is ASCII characters
<sp> is a space (0x20)
12345 is altitude in feet
<CR> is a carriage return (0x0d)

Why this is all in the 430 manual but not in the 327 manual is beyond me....

Paul
 
Thanks for taking the time Paul. I really am starting to think I definetly have a component problem. Everything with the wiring and settings is checking out. I am going to get the transponder checked at an avionics shop.. Maybe the shop will have some tool or device that I can check the EFIS out with. I really would like to get this thing running with serial data.
 
I'm not clear on what you mean by grounded.

Are the grounds interconnected between the units? As in serial ground to serial ground and not just some random grounds on the structure of the craft.
 
Yes the serial ground on the transponder (Pin 25) is wired to the serial ground on the EFIS (directly) . The transponder is also grounded directly to the airframe on pin 13. Pin 13 and 25 on the transponder are both common ground. Also the wire used is shielded and grounded at one end.
 
I had noted there was no spec for baud rate and no means to change the value. I suspect the 327 may auto detect the baud rate.

My 327 needs several minutes on before it displays the alt/fl data. I had thought this was the Ameriking (paraallel) encoder but might be the 327. How long did you wait?

How about connecting the serial signal to a laptop running a terminal program to confirm the data is present.

Doug Gray
 
Doug -- Interesting to know that it takes some time to display alt information. I will hook it back up and leave it on for a longer period of time. I am sure that I had left it on for at least 5 minutes with no data, but will give that one more try. Also where does one get this terminal program that you are suggesting, it is worth a try. Thanks for the tip.
 
The baud rates for Icarus are 9600, but check that setting a 2nd time to make sure it's on the input of the RS-232 channel and not the output, and also make sure the output is set correct on the EFIS.

Regarding the time lapse one owner saw with his encoder, that's a common thing with separate encoders, they typically can take anywhere from 2-5 minutes to "warm up". With EFISes typically the altitude will show up instantly - although we've not yet played with an MGL unit the rest of them (Dynon, GRT, AFS, etc..) all show the data instantly. The 327 doesn't have a "warm up" time but stand alone encoders typically do.

If you've verified everything above, then obviously there must be a component problem with either the EFIS or Txpdr. Not saying it can't be the txpdr (it could be), but I'd find it highly unlikely. I can't remember the last time I saw a 327 bad out of the box.....

Cheers,
Stein
 
..
My 327 needs several minutes on before it displays the alt/fl data. I had thought this was the Ameriking (paraallel) encoder but might be the 327. How long did you wait?

The waiting time before you start seeing altitude information on the transponder is NOT due to the transponder but the time to get the altitude transducer up to operating temperature. You will notice that in the summer, the altitude information comes up much quicker than in the winter. The transponder will start to display and send the altitude information as soon as it get is from the encoder ---or EFIS in this case.

If there is altitude on the MGL, there should also be altitude on the transponder.
 
One other thing to check Jarvis is something that has bitten me in the past - check the harness connector sockets very carefully to make sure you don't have one recessed. You can disconnect the harness and do continuity checks all day, confirming that the right wires go to the right places, but then when you put it back on the unit, it doesn't "make" well. Like Stein says, it is unlikely that you have bad units "out of the box" - at least it is one more thing to check!

Paul
 
Everything mentioned in all posts has been tried or checked, with no resolve. I thank all you guys for helping, but it appears I have a deeper problem somewhere. The only next step is to start checking components. I will post my resolve just FYI when I do figure it out, whenever it happens. Thanks again,
 
The Garmin 430 Install manual shows the Icarus format to be:

ALT<sp>12345<CR>

where:

ALT is ASCII characters
<sp> is a space (0x20)
12345 is altitude in feet
<CR> is a carriage return (0x0d)
Reviving this ancient thread, does anyone know what format the altitude data is in and the range? It can't be straight binary coded decimal because it's possible see negative altitudes displayed on the GTX-327. I have seen -1,000' when my system was acting up. Is that the bottom of the range?

As for configuring the GTX-327:
With the unit turned off, holding down the FUNC key and pressing one of the power on keys provides
access to the configuration pages. The FUNC key sequences through the configuration pages. The
START/STOP key reverses through the pages, stopping at the first configuration page. The CRSR key
highlights selectable fields on each page. When a field is highlighted, numeric data entry is performed
with the 0 ? 9 keys and list selections are performed with the 8 or 9 keys. Press the CRSR key to accept
changes.
Pressing the FUNC key displays the next configuration page without saving the changes.
Configuration page changes are stored in EEPROM memory. To exit the configuration pages, turn the
power off. Then turn on again (without holding the FUNC key) for normal operation.
Do not fail to press the CRSR key when you're done making changes, or they won't be saved. Ask me how I know :rolleyes:
 
Idea

I've been thinking that this would be a great business opportunity for some enterprising soul: Design and build a small electronic device which would decode and display the serial altitude output from an encoder. It seems like it would be pretty straightforward. Just a clock, a shift register, some logic to sync the register on the ALT_ word, a decoder, and a display.
 
My GTX-327 has been working flawlessly with serial altitude input for a couple months now but yesterday it suffered a new kind of failure. When started up and turned on the avionics master, the transponder didn't come on. The screen was dark. I pressed the ALT button and the screen came alive with the self-test screen, then went dark again. I went through this process several times with the same results. After doing my runup, the transponder seemed to stay on, and it did for two trips around the pattern. The Reply symbol was acting normally so I figured the box was working. Has anyone ever seen a GTX-327 act this way before? What would cause the unit to shut down during the self-test?
 
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