Handheld GPS - Losmandy Gemini
Making a connector cable to marry
Garmin eTrex GPS to Losmandy Gemini PC Serial Cable
Aim of this exercise: To have
GPS support that provides the Losmandy Gemini GPS
information upon start-up.
This is a simple advice to those, who
like me, have been challenged marrying a handheld GPS device
to the Losmandy Gemini System. It is important to note,
there are commercially available alternatives that provide a
dedicated solution.
In my case, I purchase the Garmin
eTrex, and the Garmin serial adaptor for the eTrex to ensure
a good connection to the handheld device. The price of these
two items (at the time of writing: Oct 2009), was about
AUD$150.00. You will also need a new RS232 9 pin serial plug
(male end).
In regard to the Garmin serial adaptor, there are instructions on the web
on how to make the special adaptor yourself, so just have a
Google search to find one of the alternatives.
This instruction also assumes that you have the
PC serial connector cable for the Gemini [see below...], that you can strip
and solder cables, and perhaps have a multimeter to check
your wire connections.
Image A. Standard serial PC adaptor cable
for Gemini System
The serial adaptor for the Garmin eTrex
has at one end the specialised connector to connect to the
eTrex [see image C below], and the other end, a 9 pin RS232 serial plug. To
start off, you’ll need to cut off the serial plug, leaving
the majority of cable with the specialised eTrex plug. Clean
and strip the cables for soldering to the serial plug –
there are THREE (3) cables in the adaptor.
The plug for the eTrex is made up of
FOUR (4) connector points, and can be seen below (NOTE: Pin
ONE(1) Not in use!). There is a groove in the Garmin plug,
which ensures the plug correctly slides into the eTrex. This
also helps to identify which is pin 1-4:
4 pin Garmin custom connector
The pinout information of the Garmin
plug is as follows (I have included the colours of the
cables in my Garmin adaptor):
- NOT USED!
- Data IN (RS232 RX) - YELLOW
- Data OUT (RS232 TX) - WHITE
- Ground - BLACK
Next the pinout information is for the
RS232 Serial plug (male):
Image B.
In this case, only pins 2, 3 and 5 are
used for the serial plug:
- YELLOW
- WHITE
- BLACK
See below (please excuse my serial
plugs condition, it was salvage from another cable):
Image C.
Next, you must finish off your cable by
installing the cover over the serial plug end.
Last thing to do, set up your eTrex to
transmit in "TEXT OUT" at a serial port speed 4800 via the "Setup" menu,
then "Interface" option. Next make sure the Gemini also
communicates via its serial
port at 4800.
And you are finished! Now you can
connect your eTrex to your new adaptor cable, then the new cable to
the standard Gemini PC serial cable, and then the PC serial cable into the
Gemini.
Instructions on how to make the Gemini
PC serial cable can be found in the Gemini L4 manual.
Steve Mohr
