I wrote about how I was monitoring my position with a GPS and then later using software to tag those positions to each photograph based on the time stamp.
What I didn’t mention is that you need a cable to connect the GPS to the computer. For this, Garmin charges you US$25 a piece.
In Singapore, who knows? S$30-50? More?
Furthermore, this stupid cable is a serial cable, not USB, which means it’s pretty useless on a Mac. More so it’s a damn slow way of communicating with the PC.
Okay, speed we can’t help. (Slow Garmin.) But we can try to save a bit of money.
So after searching around on the ‘net, I found some resources that helped me put a GPS cable together.
Parts I needed:
- 9 pin serial connector with plastic case S$2
- 25mm stereo connector and cable S$4
- Ready made serial to USB connector S$5
Equipment I needed and had:
- Screwdriver
- Soldering iron
- Solder
Does this serial connector look familiar?
Blurry outside:
Blurry inside:
Plastic case where the connector goes into:
That’s because this is the same connection that we used for our old dialup modems. (Yes, remember back in the day when we turned our noses at 14.4k modems and threw around numbers like 33.6k and 52k?)
This is a photo that shows the difference in size between a 35mm stereo plug and a 25mm stereo plug, green and black, respectively, for those of you who are not colour blind.
So basically, I cut the 25mm stereo cable. Now I have two connectors with wires. Save the one half end. You can always make some other connector. Like a 35mm to 25 mm stereo adapter.
With the other half, I strip the black case around the wires to reveal 3 other wires. Red, white, black. Red = Right, White = Left and Black = Ground.
Let’s be very clear here. The half of the wire: One end has the connector, one end has bare wire. Do not. I repeat do not cut the connector off and strip the wire, you’ll just end up with wire. Strip the wire only at the bare wire end.
This colour code system pretty much works for connecting your hi-fi speakers. Whenever you are faced with red and white or red and black connectors and don’t know which goes into the left or right side, just remember Red = Right.
Okay, back to the internals of the stereo wire. As usual, I cannot find any black wire, so I assume those strands of free copper wires will make up my ground. So I gather them together and twist them.
Then I proceed to strip away part of the red and white sleeves to reveal the copper underneath it. Again, the free wires are twisted together for each colour.
Now, I take out the solder and solder the wires to the right pins.
Easy enough right?
Unfortunately, for idiots like me, when you’re given a chart like on this page, which side of the pins do you count? On the inside, or on the outside?
The answer is, count the pins on the inside.
Better yet, just follow this picture.
Now put together everything and you’ll have a working connector for much less than US$25 and with the USB to serial adapter, it’ll also work on your mac.
Unfortunately, mine didn’t work.
Trust me to DIY stuff and never have it work the first time. Never does I tell you. But my misery is your gain.
Some people suggested that sometimes these stereo wires are wrongly wired. That is, the manufacturer didn’t learn that Red = Right.
So, if the cable doesn’t work, the swap the red and white cables.
STOP!
Because for me, swapping the wires failed too.
The real problem was, the protocol that Garmin and the GPS software of choice uses to communicate.
So, before you go on re-wiring the connector, make sure you have the right protocol to communicate with the PC.
How do you test that?
You can try with the GPS software and the GPS unit. But that’s not the best way.
The GPS software has many protocols it can use to communicate with your GPS. Your GPS unit also has several to choose from. Trying the combinations is hard.
The key here is to eliminate one end – that is the GPS software side. This way, you only have to select the protocols on the GPS unit.
And to do that, you use HyperTerminal.
What the hell is that? Well, most people don’t use HyperTerminal on their PC although it has been there since… well, forever. I remember using it on Windows95.
If you ask me to tell you what HyperTerminal is exactly, I can’t. I can only tell you that I used it to communicate with other computers. Even talk to my modems directly like typing commands like “AT&S” or “AT&H”. I used HyperTerminal to troubleshoot a lot of my modem blues.
Don’t ask me what those commands mean now, but with those instructions, I could tell a modem to convert its signal to pulse mode, disable call waiting and call someone else’s line, and then use the top speed to communicate. Then I could also tell the modem to hang up.
Even if people use dialup now (such as my uncle in KL) to communicate on the Internet, all these commands are still being used. But because of sophisticated software, it all happens behind the scenes.
I also used HyperTerminal to connect one PC to another PC to network it using a null modem cable – a modified serial cable – that, at that time was a much cheaper solution than purchasing an ethernet card and using an ethernet cable.
Using null modem cables, I transferred data from old Mac Classics to my DOS or Windows PCs.
Okay, back to the GPS cable and how to ensure that the GPS unit is sending communication signals to the PC.
Fire up HyperTerminal. (Um, that’s in the Accessories > Communications menu.)
Just create any connection. It’ll ask you for a name, just type in anything because you won’t be saving this connection, nor will you be referring to it once your cable works.
Once you are in HyperTerminal, in your GPS unit, select a protocol to communicate with your PC. When one doesn’t work, select another. Cycle through all. If you have chosen the right protocol, you’ll see funny symbols running across the screen.
That’s it. Now you know for sure that your GPS unit is talking to the computer and what protocol it uses.
Now, if that doesn’t work yet, don’t give up on HyperTerminal. For each protocol that you test on the GPS unit, open and close a different connection on HyperTerminal.
Fully exhaust this method first.
From my experience it is a protocol error rather than a wiring error (unless your solder is so weak, the wires have fallen out) that is the problem.
Once you have discovered the protocol that the GPS unit is sending signals to your computer, you can forget HyperTerminal.
Now, fire up the GPS software, select the GPS software protocol to match the GPS unit and you will be able to download and upload tracks, waypoints and so on to the computer.
If the GPS cannot talk to HyperTerminal at all, then the stereo cable has indeed been wired incorrectly. Swap the Right/Left wires on pins 2 and 3 on the serial connector, and it should work.
If it doesn’t, then you probably didn’t do the HyperTerminal test right. And there’s only two avenues for you to take. Start again or fork out the US$25 and get the real thing.