On Mon, 30 May 2005 17:06:59 -0700, "Anonymous"
wrote:

Hi, Everybody,

I am trying to set up an APRS station consisting of a Garmin GPSmap 60 and
one of the TinyTrak3 TNCs. However, the green 'GPS Valid' LED never lights.

I can connect the GPS receiver directly to my computer's serial port and
read good data, and I can capture some of that data and play it back from
computer to TinyTrak and the green LED lights up, but a direct connection
between GPS and TT just does not work.

I see a waveform coming out of the GPS serial (J2 pin 2 of the TT) using a
scope. Quiescent voltage is -5V, and when the data burst comes it is -5 V to
+5 V.

Could this be a voltage level problem on the serial? Is there a converter
that can be used? Or is it another problem, possibly protocol-related?

Any ideas?

Thank you,

Al W6LX


OK Al, I'm going to go out on a limb here. The GPS doesn't work on
the TNC. It does work on the PC. The PC can send GPS data it
recorded from the GPS out to the TNC and the TNC recognizes the dya as
GPS data and interprets the protocol correctly (the green LED goes
on). You measured the waveform from the GPS and it shows +- 5V.

I. The GPS is good, it works on the PC.
II. The PC is good, it reads and writes GPS data.
III. The TNC is good, it reacts correctly to the PC and the GPS data
from the PC.
IV. The GPS waveform is +- 5V.

My conclusion: The voltage is too small for the TNC to recognize.
Did you 'scope the PS serial data? If you do, you will see that it is
+- 12V. The PC's serial port can read and write both +-5V and +-12V
levels. You need a level converter to change the GPS data to the
level that the TNC needs to see.

Russ