Thorp Air Command -

Supporting Owners, Builders and Pilots of the Thorp T-18 and its variants.
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PostPosted: Mon Apr 06, 2020 10:20 am 

Joined: Sat Aug 05, 2017 11:52 pm
Posts: 35
Hey Folks,

I just wanted to share some notes on the GRT EFIS/Garmin 175/EchoUAT install that would have made my install much easier. I figured this is a good platform to share it for other Thorp builders and the larger cosmos of builders. I know that numerous wanna-be Thorpers have had similar issues. ;)

My serial setup was:
Serial 1: EchoUAT ADSB in, stand alone GRT Safe-fly GPS
Serial 2: RS 232 Input for the Garmin
Serial 3: ARINC 429 Module

From Jeff at GRT:

The 175 has two ARINC inputs and only one output. The EFIS also has two ARINC inputs and only one output.

Here are our notes on the 175 connection and setup. I've adjusted them for your use of Port 3 and the passthru port.

The GPS175 pins are on the J1751 connector.

RS-232 connection
GPS175 Pin 9 (RS-232 OUT 1) -- any serial input on EFIS or module
Example: GPS175 Pin 9 (RS-232 OUT 1) -- GRT ARINC pin 8 (Serial Input pass-thru on male D-sub on box)

A direct connection to the display is preferred unless you're out of serial ports.

ARINC connections
The GRT ARINC-429 connector (female D-sub on external module box) will be referred to as the C connector here.
GPS175 Pin 5 (ARINC 429 OUT 1A) -- GRT ARINC pin C1 (ARINC 429 IN 1A)
GPS175 Pin 6 (ARINC 429 OUT 1B) -- GRT ARINC pin C2 (ARINC 429 IN 1B)
GPS175 Pin 27 (ARINC 429 IN 1A) -- GRT ARINC pin C5 (ARINC 429 OUT A)
GPS175 Pin 28 (ARINC 429 IN 1B) -- GRT ARINC pin C9 (ARINC 429 OUT B)

(Any other RS-232 input/output and ARINC-429 input/output can be substituted.)

GPS175 Settings:

ARINC RX Port 1:
Format: EFIS/ADC
Speed: Low

ARINC TX Port 1:
Format: GAMA Format 1
Speed: Low

RS232 Port 1: Aviation Output 1

The 175 does not have an RS-232 Fuel/Air Data (FADC) input like other Garmin IFR GPS units. There's no serial output to configure on the EFIS.

EFIS Settings in SET MENU, General Setup:

For units with external ARINC module: ARINC Module Connected: Yes, Port 3

ARINC Receive Rate: Low
ARINC Transmit Rate: Low

Serial Port Rate: 9600
Serial Port Input: GPS1 Aviation/MapCom
The Serial Port Output is not used for the 175 and can be used for unrelated functions at 9600 baud.
Using GPS1 for the GPS175 is recommended and sometimes required. Change any other GPS to GPS2.

If the GPS RS-232 is connected to the pass-thru port (pins 8 and 9) on the external ARINC module male D-sub,
configure the serial port that the ARINC module is connected to as 9600 GPS1 Aviation/MapCom.

For example, if the ARINC module is connected to port 3, the settings would look like this:
ARINC Module Connected: Yes, Port 3
Serial Port 3 Rate: 9600
Serial Port 3 Input: GPS1 Aviation/MapCom
Serial Port 3 Output: Off (not used by the 175, you can use it for something else)

Other settings in General Setup:

This tells the EFIS to use the GPS data from the ARINC-429 connection when GPS1 is selected.

NAV Mode Source: Internal
The GPS175 does not have a built-in VOR/ILS receiver, so all mode changes must be done in the EFIS.

GPS1 Flight Plan Source: External
This tells the EFIS to use GPS flight plan data from the GPS175 RS-232 connection.

GPS2 Flight Plan Source: update this to match your GPS2, if any.
GRT GPS units should be Internal. GPS units that transfer flight plan data should be External.

Virtual GPS2: Normally Off unless you know you want this feature.
If you have two GPS inputs this must be Off.

Settings in SET MENU, Primary Flight Display:

To enable the approach modes and PFD indicators, you must configure the ILS display:

ILS Type: pick Needles or Scales as preferred
When some other features are turned on, only Scales mode is possible.

Show VOR CDI on Localizer: No, unless you have a VOR input.

Show GPS CDI on Loc/GS: Yes
This displays the GPS approach deviations on the ILS indicators.
This is required for the GPS approach display and capture modes in the EFIS.

For the ARINC module on port 3 you would have the male D-sub pin 4 connected to EX pin 23 and male D-sub pin 3 connected to EX pin 25.

For the EchoUAT/GRT Safefly combination, there is an unpinned wire inside the connector supplied by GRT that needs to be pinned for standalone (no EFIS control) operation. It isn't called out in any of the manuals except in the wiring diagrams in the GRT Safe fly manual.

Hope this helps someone! I ended up taking my panel apart 6-9 times to try and troubleshoot the ARINC 429 module and ADSB out difficulties.


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