VisorCentral.com (http://discussion.visorcentral.com/vcforum/index.php)
- How To / Troubleshooting (http://discussion.visorcentral.com/vcforum/forumdisplay.php?forumid=2)
-- Garmin GPS (http://discussion.visorcentral.com/vcforum/showthread.php?threadid=2716)

I was having trouble getting my GPS to work with the Visor serial cradle. When I tried to initialize GPS communication by using the "start button" of Quo Vadis GPS mapping software, I lost synchronization after only 6 NMEA sentences every time - after only 5 seconds!
After some experimentation though, I was able to get the Visor/Garmin GPS 12/Quo Vadis combination working by taking apart my serial cradle and soldering a lead to the PCB connector that goes directly to pin 1 (RXD) of the Visor. I soldered another lead to the PCB connector that goes directly to pin 4 (ground) of the Visor.

The GPS communication and autoscrolling works perfectly if I do the following connection sequence:

1. Directly connect pin 1 (RXD) and pin 4 (GND) to the GPS 12 via the above soldered leads and initialize my Visor GPS software (i.e., tap "start" in the GPS window of Quo Vadis)

2. then disconnect the directly connected pins 1 and 2, and then reconnect the Visor serial cable to the GPS 12.


The GPS 12/Visor/Quo Vadis then works perfectly. The messages window scrolls continuously with NMEA messages and never stops and the auto scrolling mapping function scrolls perfectly along with your GPS position as you change position.

Step one above must somehow "synchronize the frame" (maybe with a sync pulse or handshake?)in order for continuous NMEA communication with the GPS.

By the way, I tried several other software package demos (i.e., Atlas, Placetrace, etc.) and I experienced exactly the same problem. The technique I described above worked perfectly for these programs also. I have to believe this framing problem is related to the circuitry in the cradle (it's certainly not the software). I understand that it's TTL and not RS-232, if this makes a difference.

Hi:

Neat solution, but I'm a bit confused. What is not clear is how you connect and disconnect the leads. Do you use a momentary switch wired to the PCB, or a wire to jumper the two pins?



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Mike Vidal
Ice Owner
Corvette Enthusiast
Racecar Spelled backwards is Racecar!

Hi:

Neat solution, but I'm a bit confused. What is not clear is how you connect and disconnect the leads. Do you use a momentary switch wired to the PCB, or a wire to jumper the two pins?



------------------
Mike Vidal
Ice Owner
Corvette Enthusiast
Racecar Spelled backwards is Racecar!

Regarding my Garmin GPS, this is how I set this up on my serial cradle:

I attached the soldered leads I described to a female DB9 connector, cut a hole in the side of the cradle (at the base) to accommodate the DB9 connector (drilled two screw holes, too), and attached it.

So, I perform step #1 above by connecting the Garmin GPS (I put a male DB9 connector on the end of the Garmin cable) to the DB9 on the side of the cradle. I then disconnect it and then perform step #2 which connects the Garmin GPS to the standard DB9 that's on the end of the Visor serial cradle cable. NMEA sentences then start scrolling continuosly in the NMEA messages window on the Visor and GPS location fix commences and your position is locked in (works great with Quo Vadis, Atlas, Placetrace, etc.).

It's awkward, but effective!(at least it works with the Garmin 12). I haven't tested other GPS makes/models but I suspect the same will hold true. I believe GPS receivers require true RS232 to communicate, not TTL. This seems to be a simpler way to get around the TTL vs. RS232 issue that everyone seems to be having with the Visor serial cradle (without having to add a TTL to RS232 converter and battery - yikes!).

In the car, I just use a rubber band to hold my Visor in the cradle and my Garmin hangs from a rubber suction cup attached at the bottom corner of my windshield. I could use it on my boat, but alas, I don't live in Florida anymore - not much use for GPS on a lake here in Texasville!