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Matt Dralle
Site Admin
Joined: 08 Nov 2005
Posts: 25704
Location: Livermore CA USA
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 Posted: Fri Jan 02, 2009 10:41 am Post subject: GPS Serial Data to Garmin GTX-327 Transponder |
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Listers,
I've tried sending two different sources of NEMA 0183 data at 4800/9600/19200/38400/57600 baud rates to my Garmin GTX-327 on both serial input ports 1 (db25 Pin 2) and port 2 (db25 pin 19), and configured for "GPS" input. But I don't get anything on the 327 serial input test display. I have been successful at getting AirData Z-format from the GRT EFIS at 9600 baud into either of the GTX-327 serial ports, so the ports are good. The GTX-327 just won't seem to see the GPS data for some reason.
Am I doing something wrong? Has anyone else tried this successfully?
Thanks!
Matt Dralle
RV-8 #82880 N998RV
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Matt Dralle
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GrummanDude
Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA
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| Posted: Fri Jan 02, 2009 12:44 pm Post subject: GPS Serial Data to Garmin GTX-327 Transponder |
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Call Jeff at (661) 949-8300
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Gary
AuCountry Aviation
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douglist(at)macnauchtan.c
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| Posted: Fri Jan 02, 2009 1:23 pm Post subject: GPS Serial Data to Garmin GTX-327 Transponder |
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At 10:39 -0800 1/2/09, Matt Dralle wrote:
| Quote: | I've tried sending two different sources of NEMA 0183 data at
4800/9600/19200/38400/57600 baud rates to my Garmin GTX-327 on both
serial input ports 1 (db25 Pin 2) and port 2 (db25 pin 19), and
configured for "GPS" input. But I don't get anything on the 327
serial input test display. I have been successful at getting
AirData Z-format from the GRT EFIS at 9600 baud into either of the
GTX-327 serial ports, so the ports are good. The GTX-327 just won't
seem to see the GPS data for some reason.
Am I doing something wrong? Has anyone else tried this successfully?
|
I recently had experience with a Garmin 425 GPS (a tiny one not
really for aircraft use) that claimed to put out RS232 compliant
signals.
What I discovered, with an oscilloscope, was a signal level that was
"low" at about +150 mV and high at about +4.5 V with a fairly high
internal resistance that had problems at 1 mA output levels. Without
careful grounding at the pins of the GPS the +150 mV was even worse.
RS232-C, which is the only official RS232 spec I can afford right now
calls for a negative going level for the low value and Garmin simply
does NOT meet that. There are some newer RS232 specifications around
that might describe Garmin's output level but when I asked all I got
was "RTFM" and the PDF manual simply says RS232 compliant.
I placed a 1.5 volt dry cell in series with Garmin's output with a
polarity that subtracted 1.5 volts from all signals. The resulting
data stream went negative and was acceptable to the old Macintosh I
was working with at the time. Some USB to RS232 converters would
work and others would not.
You seem to be talking about the Garmin as a receiver rather than a
transmitter and I have no idea how well Garmin's "RS232 compliant"
receiver behaves. I do doubt that you will get an authoritative
answer from them.
--
--> A fair tax is one that you pay but I don't <--
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