Transponder Serial Connection Question

jrvssgl · #1 07-13-2008, 10:36 PM

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.

Ironflight · #2 07-14-2008, 05:18 AM

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

jrvssgl · #3 07-14-2008, 12:21 PM

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?

w1curtis · #4 07-14-2008, 12:54 PM

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.

jrvssgl · #5 07-14-2008, 01:34 PM

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.

SteinAir · #6 07-14-2008, 02:18 PM

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

jrvssgl · #7 07-14-2008, 06:20 PM

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

vlittle · #8 07-14-2008, 07:17 PM

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

jrvssgl · #9 07-14-2008, 07:51 PM

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?

Ironflight · #10 07-14-2008, 09:10 PM

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