Cambridge L-NAV and S-NAV

Our UK agent Dickie Feakes is greatly knowledgeable about the old Cambridge instruments. He put together the following tutorial about how to connect an L-NAV and S-NAV to Oudie: Data Sheet No 7: Connection of Oudie to a LNAV, SNAV , LXNAV or a C3/C4

A Cambridge LNAV or SNAV needs a GPS data stream that includes the details of a GOTO waypoint if it is to display correctly.   In the past this data has been provided by either a Cambridge GPS10, GPS20, GPS25 system, or a Garmin GPS unit.   It is now possible to interface an Oudie with an LNAV or SNAV so that it provides full functionality of the LNAV using GPS waypoint and GOTO data from the Oudie.  However, it should be noted that this feature is only implemented when using the internal Oudie GPS at 4800 baud.   If an external GPS is used, such as a Flarm unit at 19200 baud, then this feature is not available

Oudie can also supply GPS data to a LXNAV and the C3/C4 vario systems.   Although the LXNAV reports the status of the GPS correctly, the number of satellites shows “0”.

The hardware requirements are:

1.   An Oudie running firmware v4.10.013 or later

2.   A modified Oudie profile file

3    A data lead to connect the Oudie RJ45 plug to the LNAV, SNAV or LXNAV RJ12 Datacom socket

Preparation of the Oudie

The Oudie should be running V4.10.013 or later.   If the Oudie is running an earlier version of firmware it can be upgraded from the See You website,

A modified Oudie profile is required and this is best achieved by creating a new profile with the title LNAV.   To do this start Oudie, select Menu/Settings/Next/Next/Next/Misc and tick the “Add Profile” box.   Select “Copy current profile” and using the keyboard, alter the new profile name to “LNAV”.  Press OK

Modifying the Oudie Profile File

Now with See You Mobile running, connect Oudie to your PC with the PC data cable and select “Connect to PC” when it comes up on the screen.   If you now access My Computer or Windows Explorer on you PC, you will find a disc drive called “TFAT”.   This is Oudie and you will see a folder titled “Settings”.   Open this folder and you will see the LNAV.xml profile.   This profile now needs modifying and this is best done with a text editor such as Wordpad, which is found in every Windows OS computer.  Open Wordpad and select “TFAT/Settings/LNAV.xml” .   Do not forget to click on “Files of Type” and select “All documents” otherwise you will not be able to find the LNAV.xml file in the Settings folder.  Open the LNAV.xml file  and scroll down to locate the heading <SERIALREADER>.   A few lines below this you will see a line <COMOUTPARAMS/>. Edit this line to read <COMOUTPARAMS>COM4:4800,N,8,1</COMOUTPARAMS>.  Then click on File/Save on the menu bar and the new file will be saved to Oudie.

If this is too difficult, then you can simply click on this LNAV.XML tag and transfer a modified profile from my website .  Ensure it is transferred  into Oudie by writing it into the  TFAT/Settings folder.

Ensure that you have Oudie configured to run using its internal GPS by selecting COM1 in Menu/Settings/Next/Next/Next/ Hardware

Data Lead

All that is needed now is a modified data lead to connect between the RJ45 of Oudie and the RJ12 socket of the LNAV/SNAV/LXNAV.   Configuring this lead is potentially hazardous as if you get it wrong, 12volts from the Oudie can be fed to the data input socket of the LNAV causing mayhem.   A correctly configured data lead is available at £17 from Bicester Aviation.   However, if you want to do it yourself proceed as follows;

Hold the six pin RJ12 plug with the tag on the top in front of you so that the 6 way cable  is coming out towards your stomach.   Looking down on the plug, the right hand land is pin 1.   The left hand pin (which is pin 6) is data negative or ground.  Pin 4 is data into the instrument.   Identify the leads from pins 4 and 6 and mark accordingly.

Holding the Oudie RJ45 in the same orientation as above, the left hand pin is pin 1 and the right hand pin is pin 8.   Data negative/ground is pin 7 and data out is pin 6.  Identify these 2 leads and mark accordingly

The respective data negative/ground wires and the data positive wires are now connected.    No other wires should be connected.   The RJ45 plug is now connected to Oudie using one of the RJ45/RJ45 connectors supplied in the Oudiebox.   The RJ12 is plugged into the datacom socket.   With both devices powered up, the GPS flag should go from “Off” to “Wait”.   Once the Oudie has locked on to the GPS, the data should be displayed in the LNAV, SNAV or LXNAV

Updated on March 17, 2021

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