Building GPS
Data Cables and
Power Cords
AGPS 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
Although most GPS units have an interface for a cable connection, bear in mind that not all do. This is especially true of some of the less expensive units. When in doubt, consult the manual.
In addition, when buying a new GPS receiver, it is generally uneconomical to choose one that does not have a cable interface, as the savings will be small, whereas the return from having an interface will be huge.
chapter
in this chapter
˛The right cable for the right application
˛Combining multiple cables
˛Making your own cables
˛Connecting to a PDA
14 Part I — Hardware Hacks
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.
Figure 2-1 shows a PC-to-Garmin eTrex data cable.
FIGURE 2-1: A PC-to-Garmin eTrex data cable
Chapter 2 — Building GPS Data Cables and Power Cords |
15 |
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. Figure 2-2 shows a data cable for an iPAQ Pocket PC.
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/cgibin/P/USB_G4).
Make sure that whatever converter you get has drivers to support the operating system you are running on your PC.
Bear in mind that there are several different kinds of GPS connector. Figure 2-3 shows two of the most common ones.
FIGURE 2-2: An iPAQ-to-Garmin eTrex data cable
16 Part I — Hardware Hacks
FIGURE 2-3: Two GPS connectors
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.
Not all GPS receivers can handle a direct 12-volt power input and can be seriously damaged. When in doubt, check!