HOME  :: WHAT'S NEW :: PROJECTS :: SAILING :: MAINTENANCE :: RESOURCES  
  THE REBUILDING  ::  SMALL PROJECTS  ::  TECHNICAL  


Electronics (Page 3)
This page was last updated on 9 May 2002.

Knotmeter/Depthsounder     GPS     VHF     Radar     Laptop Computer and GPS Interface

Return to Page 1          Return to Page 2

Laptop Computer and GPS Interface

I am a traditional navigator, in the modern sense.  What does that mean?  Well, it doesn't mean that I'm going to navigate with a sextant, although I do know how.  Of course I'm going to use GPS, and for a failsafe I have a second GPS.  My main GPS has a plotter with G-map cartridges, and these provide sufficient detail to assist in easy navigation.  It's very cool.  However, I never rely completely on anything electronic.  You can't navigate without real charts, and I have real NOAA charts for the whole Maine coast on board.  I love charts--love 'em!  Anywhere we ever go, I will have the proper paper charts on board.  Chart Kits are OK, but nothing beats a real chart.  Did I mention I love charts?  I really do.

That said, I also like gadgets and such, to an extent.  When an opportunity arose to acquire one of the best navigation software programs--The Cap'n Voyager--I jumped at it.  Although I will never rely on this program (after all, I love charts), it is undeniably cool.  It's designed to be interfaced with GPS, to show your ship's position right on the chart on the screen.  In addition, it has all kinds of routing and planning features, and makes navigation a snap since you can place waypoints at the click of a mouse and navigate directly to them.  Way cool...but I wouldn't dream of relying on this.

With the Cap'n, I got a CD that contains all (all!) of the NOAA charts between Block Island, RI and the Canadian border.  That's a lot of charts, and it's been fun over the winter to browse through them on the screen.  (I love charts.)

A while back, I purchased a Dell  laptop computer (Pentium II, 266 MHZ; 128 Mb RAM).  I wanted this so that I could write on the boat, keep logs, download photos, update the website (from shore), etc.  

The navigation program is set up to allow a comprehensive NMEA 0183 interface between the computer and the GPS, for dialogue back and forth and sharing of pertinent information.  With this capability set up, the program reaches new heights of convenience and usefulness.  It should be easy to set up the interface--after all, both GPS and computer are designed for it.  Right?

Yeah, right.  

backopgps.JPG (152025 bytes)When I installed my GPS, I purchased a mounting bracket and external DC power/data cable from Garmin; the way the GPS 175 is set up, there is a flush set of gold contacts on the back, and the power/data cable, with small, spring-loaded pins, contacts these when you install the GPS in the bracket; the cable is screwed to the bracket.  This is all well and good.  After I bought the laptop, I also purchased, from Garmin, a PC interface cable.  Well, as it turns out, installation was hardly so hunky-dory.  The first thing I found was that basically I didn't need to have gpsbracketmount.JPG (175157 bytes) bought the interface cable; the original power/data cable I bought has all the wires needed for NMEA connections.  Second, use of the interface cable, as supplied, is mutually exclusive with use of the original power/data cable; there's not an extra plug or anything on the back of the GPS.  This whole thing stumped me for a while--at first, I couldn't see how I could possibly interface and supply DC power to my GPS.  Then, it seemed that there was no way  that it couldn't be possible--that would simply be too dumb.  Well, it's not quite that dumb--but almost.

After some research online at the Garmin website and in my Garmin manual, I figured out that I could make this all work--the power/data cable that I already had attached contained all the necessary wires.  OK.  So, all I had to do was cut off the GPS end of the new PC interface cable (which has a DB9 serial port at the other end for computer connection) and connect the appropriate wires.  Simple.

Instantly, I ran into a problem that would prove to be difficult to get past (well, at least until I had an epiphany later on).  The wires inside the GPS power/data cable are all color-coded--from the wiring diagram on the Garmin site, the ones I wanted were blue, brown, and the ground (black).  That's helpful.  I thought that, given that the PC cable was from Garmin and intended for connection to this GPS, that it would probably contain wires that were the same color.   Think again.  It turns out that the three wires inside the PC cable were white, black, and yellow.  So much for a nice, simple connection.  Am I crazy, or wouldn't it have made sense to have blue, black, and brown wires inside the PC cable?

OK, I thought, I'll just peek inside this serial connector somehow and see which wire goes to which pin.  A DB9 connector, for those who don't know, is the small 9-pin connector that you might use to connect a modem to the back of your computer.  The computer has the male connection, with external pins, and the cable has female pins.  Each pin is numbered according to a standard.  I only had to figure out three wire colors; the other pins in this particular cable had no wires connected, as they were not needed.

 

Well, have you ever tried to take one of these connectors apart?  It's a molded plastic head, with the wires inside.  After looking at it, I slowly pried up the face of the plug, and it started to come out.  Cool, thought I, the innocent, I'll just keep slowly pulling this out, and it will pull the wires with it so I can see what wire goes where.  Then I'll be on my way.

As you are probably guessing, this was not the case!  What actually happened was that the stupid little wires pulled right out of the backs of the pins, since the whole mess inside is encased in a semi-hard plastic.  There was no way I could see which wire went where, and, of course, this ruined the connector anyway--there was no way to reinstall it.  Sigh.

Moving on.  I had trashed one cable, but I wasn't dead yet.  Next, I researched online, looking for a wiring standard for DB9 connectors.  I thought I struck gold--I found a few sites that contained this information.  Since I happened to have another standard serial cable with two female ends, that I had purchased for some other computer use, lying around the house, I figured I could cut off one end, and then, using the wiring information I found online, determine the correct wire colors for each pin, and then simply connect the wires to the GPS cable.  Seemed logical and simple enough--between the wiring information from the Garmin site and the new "standard" wiring colors, it would be a breeze.  Psyched, I made up the connections on the boat, crimped and sealed, and arrogantly tied up the wires and cleaned up the tools before proceeding.  After all, the wiring standard had to be right, right?

Wrong.  Of course.  Why would it be right?  I could not get the GPS to be recognized by the nav program.  I tried everything.  Apparently, the wires were wrong.   Double sigh.

Still kicking, I tried one more plan--a surefire way to make this work.  The serial cable I was now using had had two female ends...one was still connected, and would remain so, but the other was sacrifice-able.  A little cautious dissection and surgery, and I could figure out if the wires ran to the pins as they were supposed to according to the DB9 "standard", or else figure out which wire color went where.  Then, since I had to assume that each end of the cable (with identical connectors) would be wired the same way.  

With a sharp serrated knife, I carefully cut through the plastic connector housing and removed it without too much trouble.  Now, I was faced with a rubbery block of junk that encased the individual wires and the backs of the pins.  I could see some of the wires swirling around at the surface, taking illogical paths to God knows where.  Ever so slowly, I pared away the rubbery junk, taking pains not to cut any of the wires or remove their insulation so that I wouldn't be able to identify them.  I only needed to figure out pins 2, 3, and 5.  All other wires were irrelevant.  After 10 minutes of cutting (it's kind of like an archeological dig, where patient people remove hundreds of pounds of dirt with whisk brooms so that they don't damage the bones or pottery or whatever) I thought I had it.  Pin 2-brown; pin 3-red; pin 5-yellow.  Having learned my lesson before, I simply twisted the wires together this time, leaving permanent connections till I was sure.

Still, I couldn't get the program to find the GPS.  This was most demoralizing.  I tried uninstalling and reinstalling the COM1 port on the computer; I disabled the network; I manually entered information in the Cap'n GPS.ini file as some of the troubleshooting info I had gotten online indicated...and all for nothing.

My first thought was to look for a female DB9 connector that I could take apart and wire to my specifications.  I figured I could find something like this at Radio Shack.  However, it was a Sunday morning, and, as usual, I was up early.  By the time it was late enough in the morning for the store to be open (they don't open till 1100), I had come up with new plans of attack.

The first thing I did was go up to the boat and remove the GPS (it's a handheld, after all), power cable, and bracket.  It's easy to do, and I don't know why I didn't think of it before.  It was a nasty, cold, raw, rainy day, and I figured everything would be better if I worked in my warm living room instead of on the cold boat.  With all my equipment in the house, I prepared to try everything over again.  I cut back both the GPS cable and the serial cable to new, clean ends, installed new batteries in the GPS, and set it to the simulator mode to provide a "false" fix, since the antenna doesn't work indoors.  Then, referring again to my numerous diagrams and printouts, I connected the wires as I thought would be correct.  Still nothing.  After some diagnostics, I quit.  

It was about this time that I had my epiphany:  I was looking over the remains of my Garmin-supplied PC interface cable.  The cable comes with a pre-wired attachment and plastic plug connector designed to be connected to an aftermarket AC or DC (cigarette lighter plug) adapter.  I was thinking how it was too bad that it was set up this way, as I didn't want to plug my GPS into ship's power through an adapter, though if I did I could use the cable intact without worrying about the silly DB9 wiring.  Then the "DUH!" factor hit me:  why couldn't I remove the connector from the power end of the cable (instead of the difficult, PC end) and just hard wire that into the system?  Since the cable was already trashed, I cut off the connector.  Yup, two wires, red and black.

Perhaps, dear reader,  this seems like a foregone conclusion after you've read the above.  But it really didn't seem obvious to me in the slightest until that moment.  With the clarity of hindsight, it now seems idiotic that I didn't think of this sooner.  If there's one tried-and-true rule about boat projects (or nearly any project), whatever the level of frustration was the day before, it's that if you take a break and look at things with a fresh outlook the next day, a solution almost always becomes apparent immediately.

pccablebracket.JPG (180764 bytes)So, I ordered a new cable, complete.  All I have to do is unscrew the existing power/data cable from the GPS bracket mount, unscrew its counterpart from the bracket that is supplied with the new cable (not a mounting bracket--all cables for my particular Garmin come with a sort of cradle that forces the contacts together--see the photo) and reattach the new cable (with only a 4-pin connector--hot, ground, and data in/out transfer wires) to the mounting bracket in its stead.  This should take care of the wiring problems.

The happy news is that this plan worked!  I tested the setup indoor first, with the GPS on battery power--all worked fine.  I then moved out to the boat, wired up the GPS permanently, and checked it out again.  It worked!  I tied up the excess wires again and the job was done.  Phew.

Power consumption with the GPS, inverter, and laptop running was observed to be about 3.2 - 4.0 amps. 

The screen shot below is something you never want to see when you're actually out sailing; the bull's-eye is the position of the boat (on the hard at my home when this was taken).  If you see this and you're sailing in the fog, you know you are really lost!


Glissando, Pearson  Triton #381
www.triton381.com 

We recommend viewing this site with your screen resolution set to 1024 x 768 or larger.  Problems?  Email the webmaster.

1999-2014 by Timothy C. Lackey.  All rights reserved.  No duplication of any portion of this website allowed without express permission.  Permission may be obtained by emailing the webmaster.