30 Part I — Hardware Hacks
6.Add a few dots of hot glue to the wires at the top to reduce the chances of shortcircuiting, as shown in Figure 2-20. That’s it! All done!
TOP |
Hot glue
FIGURE 2-20: Hot glue keeps the wires in place.
Making Power Cords
Making power cords is similar to making data cables. The main differences between a data cable and a power cord are that you need a cigarette plug and you connect to different pins on the GPS connector.
There are some caveats to bear in mind. Not all GPS units can handle the full 12 volts from an automotive system. Connecting some units directly to the system can cause serious and permanent damage. The Garmin eTrex range and the eMap range take 2.5 volts, and 12 volts will seriously damage them. These all use the rectangular connector and as such are easily spotted. The Garmin Rino requires a 6-volt supply. Many others can take between 8 and
32 volts (usually making use of the round connectors) but there are notable exceptions — in particular, the Garmin GPS-12, GPS-38, and GPS-40, which can take no more than 8 volts.
If you have any doubt about the power range that your GPS can handle, consult the user manual. Specifications change regularly and it’s better to be safe than sorry.
If your GPS cannot take a 12-volt supply, you will need a cigarette adapter that can step the voltage down. You can find plenty of cheap sources of these, in the form of old car phone chargers or chargers for other devices. You can also find variable chargers that enable you to control the output voltage. These are very handy, as they can be used for a variety of projects (as long as you remember to set the voltage properly before each use).
Once you have a suitable cigarette lighter adapter, making the cable is easy. The power inputs into a Garmin eTrex are pin 1 (+) and pin 4 (-), as shown in Figure 2-21.
Assembly is easy, as described in the following section.
Chapter 2 — Building GPS Data Cables and Power Cords |
31 |
FIGURE 2-21: Power pins of a Garmin eTrex connector
Power Cord Assembly
If you managed to assemble a data cable, then building a power cord is just as easy. The main differences are how you hook up the pins. Pin 1 on the GPS connector is connected to the wire from the center of the cigarette lighter adapter (the power supply), while pin 4 is connected to the other wire (the ground). Remember that for most cars, the center pin in a cigarette socket is the positive terminal, while the outer is negative, as shown in Figure 2-22. If in doubt, check your vehicle’s manual.
As a safety precaution, make sure that the cigarette lighter adapter is fused to protect both the GPS receiver from damage as well as the car from the risk of fire. If you are unsure, open up the connector and see if one is fitted. If it isn’t, add an inline fuse (using a 5-amp fuse).
Testing
Make sure you use your multimeter to verify that the output voltages are correct and that there are no short-circuits that could blow the GPS unit.
32 Part I — Hardware Hacks
-ve
+ve
+ve |
-ve |
FIGURE 2-22: Cigarette socket detailed
When it’s not plugged into a GPS, make sure that the cigarette adapter isn’t plugged in, as that makes the pins of the GPS connector live. If those live pins come into contact with metallic objects, they could cause sparks, damage, and possibly a fire.
If you use a wire or needle to hold the pins in place while you assemble the power cord, it’s particularly important to remember to remove it before use, as damage could occur.
Precautions
If you have more than one GPS unit and their acceptable voltage ranges are different, remember to carefully label which power cord goes with which GPS receiver. Carelessness to details here could cause significant damage to a GPS.
The best way to avoid confusion is to label the cables carefully, as shown in Figure 2-23, and keep the appropriate cable with the appropriate GPS. Remember to always double-check before using.