Hi all,

I spent some time this afternoon trying to figure out why my FreeTrak
stopped working. I didn't really find out, but it seems to be working
again. My suspicion is that the transmitter wasn't keying up fast enough
(or something).

Anyway, as part of the diagnosis I made some nifty wiring harnesses. It
was worth the effort and quite easy because I am using RJ11 sockets for
the serial and radio interfaces. There are two reasons for using these

1) They latch
2) They are small

The second point is most important because I notice that the TinyTraks all
have "giant" DB9 plugs and housings which are often bigger than the
TinyTrak itself. Not only that, but often the retaining screws are not
present, or not used, so the connectors don't stay together.

Now that I have specified the pin order I am able to make up adapter
cables for various radios and GPS receivers. This also means I can make
test cables which I can then use to test any radio or GPS (provided that I
have made an adapter cable first).

Here's the general pinout for an RJ11 connector with 6 ways and 4
conductors (looking into the socket).

   | '''' |
  |_    _|

As well as their latching ability these connectors are cheap, easy to
assemble, and cables can be purchased cheaply from the $2 Shop and other
import stores. Often you can buy RJ11 cable assemblies with only two
wires present, in the centre pair of pins (b & c in my diagram). This led
me to choose the following pin allocations:


a - PTT
b - Ground
c - Audio out*
d - Audio in

'in' and 'out' are from the point of view of the tracker/TNC, so pin c
will be wired to the mic. connector on the radio. Pin d is wired to the
speaker output of the radio. *Note that the PTT line can be combined with
the audio out for some HT connections.


a - +5V out
b - Ground
c - Data in
d - Data out

Pin c is wired to the data out pin on the GPS (or pin 3 of a 9 pin PC
serial port). Pin d is wired to data in pin on the GPS (or pin 2 of a 9
pin PC serial port). So, this port can be used for a GPS or as a
connection to a PC serial port (for a terminal program, or some TNC

I now have two leads for radios, one for a ZARES HT, and the other for a
Yaesu VX2R. Both are terminated in an RJ11 plug. I can easily swap them
between the FreeTrak and the PIC TNC.

Similarly I have three leads for GPS units, a Navman eFrontier, a Polstar
GPS puck, and a Garmin Geko 201. They all terminate in a RJ11 plug and I
don't have to worry about the pinouts (which are non-standard across many
GPS units). For the Geko I have inserted two 1N4148 diodes in the power
line to drop the 5V supply voltage to about 3V.

I have also made two RJ11-DB9F adaptors to plug into a PC serial port, and
an RJ11 to 3xRCA plug adapter to break out audio in, audio out, and PTT.

This means I can do the following:

Plug either radio into either the tracker or TNC
Plug either radio into the PC sound card
Plug any of the GPSs into the tracker or TNC
Plug any GPS into the PC serial port*
Plug any length RJ11 phone cable between the tracker/TNC and PC serial port.
Using an RJ11 coupler I can also extend any one of these cables if necessary.

*In practice, only the Geko works for this, as it has its own power
supply, however, I will add a 5V power supply to the GPS adapter soon,
probably connected to a USB plug for power.

In addition, any other APRS gadget that I build could use the same pinout,
which means all the gear I already have could hook up to it without me
having to build yet another set of cables for each radio or GPS I have.

I could have used RJ45s, but they are just a little but bulky, and the
cables are stiffer. The 4-core flat phone cord is nicer to work with.



PS I don't really have 3 GPS receivers. Two are occasionally on loan to me.

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