Tiny Trak & eTrex GPS

APRS is a new "game" for radio amateurs. Apart from the known D-7, D-700 Kenwood where they cover this mode without external modem, the Tiny Trak is a second simple choice for tracking, simply by using a usual VHF and TinyTrak as APRS modem. However, they need a GPS in order to be able to work as mobile.

This page describes the connection of my homebrew Tiny Track with Etrex Garmin (Fig.1).

Etrex is a cheap model of Garmin. You can find it in offers between 50 - 80 $ and it is ideal, at my opinion, for this kind of application . This is the "good news"!

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The "bad-news": Unfortunately, the eTrex's output data-cable which is necessary between GPS and Tiny does not exist in offer and it is very expensive, roughly 40- 50$!
Fortunately is a simple cable and we can easily make it, as "homebrewers" !


Fig.2 above shows the connection-place into Etrex which took place in the Upper Back-side of GPS body. It has 4 contacts: GND, Data-out, Data-In & +Vcc.

Fig.3 shows my Homebrew TinyTrak. It is a very small PCB with a female DB9 connector for the connection with a GPS or PC.

Fig.4 below shows my homebrew-Plug for Etrex Gps. The smal piece of PCB has four copper strips.
This printed-board is made from thin PCB, about 0.5 mm thickness.
If the PCB is thicker than 0.5mm, then will not enter in the 2 side-slots of GPS. In this case by using a small rasp, simply "eat" the 2 edges on both sides of pcb, in order to has a thickness of about 0.5 mm.

Another point: Etrex has between +Vcc & Data-in contactors a "driver", into the plastic case (see Fig.5).

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Thus, it's necessary to make a "slot" into PCB with similar dimension, in order to enter the driver, ensuring the right admission of PCB.

I've used a piece of RG174-cable between PCB and TinyTrak. The shield connected to GND and the centre cable to Data-Out. I've not used the other 2 connections (Data-In & Vcc).
Fig.6 below shows the PCB-plug into GPS connection -place.


Fig.7 shows the PCB -piece with tracks. It's exactly 17mm wide.

Now, we suppose that you have made the PCB-plug and stuck also a male DB9 in the other end of cable, to the TinyTrak. Keep in mind, GND must be connected to Pin 5 and Data-Out to Pin 3 of DB9.

That's all - we finished?

Nooooo !

Now it will be supposed we certify that the GPS is rightly configured in order to give NMEA protocol in the Data-output.

1) Turn on the GPS. Go to "Menu" and choose "Setup"( by HighLigthing that, see Fig.8)
2) On "Setup" set "INTERFACE" (Fig.9)
3) On "Interface" set "NMEA OUT", 4800 Baud (Fig.10)


Now, you are OK 100%. After that, connect the GPS with Tiny-Trak and go Outside... "turn-on" the GPS. After few seconds or few minutes, you must have "Full scale" on bar-signal Satellite reception . Then, the GREEN Led on TinyTrak "lights", confirming the "Data-reception". It Works !

That's all folks !

Have Fun !

Makis SV1BSX (Nov. 2002)