Building GPS Data Cables and Power Cords

A GPS receiver is designed as a standalone, mobile piece of equipment you can take with you in a car or on foot into the wilderness. It wouldn’t be very useful if it needed a hard-wired connection — how often would you want to know the precise coordinates of your desktop PC? However, most GPS units can be hooked up via cables to other devices that enhance their functionality and add features that are not available on “out of the box” units.

Without cables, you can do a lot with your GPS unit; but with the right cables, you can do so much more. In this chapter, you’ll learn how to combine power cords and data cables to reduce the clutter in your outdoor kit. You’ll discover how to connect multiple GPS units to the same PDA. You’ll even find out how to make your own cables, if you can’t buy one that suits your needs.

Cables Demystified

Cables are available in numerous styles. Their differences reflect the different ways in which they are used. Typically, three types of cables are associated with GPS receivers:

Data cables

Power cords

Combo cables

No cable connection also means that you cannot update the firmware on the GPS, and thereby take advantage of bug fixes and new features released by the manufacturer.

How you acquire the cables is up to you. Shortly I will take you through the process of making them and you can also save yourself time (but not money unfortunately) by making these for yourself. The overwhelming advantage of making your own cables is that it offers you some practice with figuring out the wiring before progressing to more complex “multi” cables.

Let’s take a brief tour of the different types of cable.

The Data Cable

A data cable is pretty self-explanatory — it is a cable that is used to transfer data between a GPS unit and another device. That other device is usually a PC or some form of handheld mobile device (such as a Pocket PC device like the HP iPAQ). When connecting to a PC, the port to which the cable connects is the serial port. The connector used is usually a 9-pin D connector.

Note that not all data cables are the same. Not only won’t a cable designed for the Garmin 76 fit a GPS from the eTrex range (as you will see shortly, the connectors on the interface are different), but a cable designed to fit a PC won’t fit, say, an iPAQ. In other words, different devices need different cables to talk to other devices. The more GPSs you have, and the more varied the devices you want to connect them to, the more cables you will need.

Even with the widespread popularity of USB ports on PCs, most data cables still make use of older serial ports for data transfer. This can be a real pain on modern PCs (both desktops and laptops), whose serial ports have typically been replaced with the more versatile USB ports. If this is the case and you still want to make use of data cables, you will need to get a USB-to-serial converter and plug it into your USB port to create a serial port for the job. A good-quality and inexpensive USB-to-serial converter is available from pFranc ( http://pfranc.com/cgi-bin/P/USB_G4 ).

Make sure that whatever converter you get has drivers to support the operating system you are running on your PC.

If you want to buy a cable for your GPS, most manufacturers make such cables available. They aren’t cheap compared to making a cable yourself, but it is a quick option. Check the user manual for details — most accessories are listed there.

Power Cords

If you have owned and used a GPS for any length of time, you know how often the batteries need replacing just at a moment when you can’t replace them, such as while driving.

Power cords differ from data cables in that they are used to transfer power to the GPS unit from a battery pack, a stack of batteries, or from an automotive circuit (commonly via the cigarette lighter). Using a power cord while using your GPS in the car (or while on the move, as I’ll show you shortly) can dramatically increase the lifetime of the batteries in the device, saving you money (if you are using disposable batteries). It also reduces the load of spare batteries you have to carry for a particular trip.

You do need to be careful with power cords. The automotive system is a 12-volt system, and while some GPS receivers can handle this amount of power, some cannot.

If you aren’t sure, carefully check the documentation or user manual.

Don’t assume that power cords are only useful in cars. Plenty of small 12-volt, lead-acid batteries available can be easily carried on a belt or in a backpack.

As with the data cables, if you want to buy a power cord for your GPS, most manufacturers make such cables available. Again, they aren’t cheap, but it’s quicker than making your own. Check the user manual for details.

Combo Cables

Combo cables, as the name suggests, are cables that combine the features of the data cable and power cord into a single cable. The result is a cable with the appropriate GPS connector for your GPS unit on one end, and at the other end a cigarette lighter adapter and a connector for your PC or Pocket PC. The main advantage of a combo cable is that you can connect your GPS to a PC or other device while at the same time powering it from an available 12-volt system with just one cable. This can be extremely useful when you are using your system for in-car navigation.

Again, if you don’t want to make a combo cable yourself, the manufacturer of your unit may have one. Check the user manual.

F IGURE : A combo cable combines data and power functions.

Combining Cable Types

So far, we’ve looked at one type of combo cable — a data/power combo cable — but there are many possible types. Here are a few possibilities:

Multi-GPS data cable: A cable that can be used on more than one GPS unit

Multi-data cable: A data cable that can connect to multiple devices

Multi-data/power cable: A cable that can connect to more than one device and provide power

Multi-data/power/GPS cable: A combo of all of the above.