Making Your Own Data Cables

Now that you are familiar with the different types of cables that you can combine with your GPS, it’s time to take a look at how to make some of them. I’ll begin by taking you through the process of making a data cable. Specifically, this data cable is one for a Garmin eTrex GPS unit.

Materials You Will Need

To successfully build a data cable, you will need the following supplies and tools:

 A suitable connector for your GPS (these are available from www.pfranc.com or www.lynks.co.uk ).

 A cable with a 9-pin D connector on the end — any old serial port cable will do, such as an old mouse or modem cable. Failing that, you will have to buy a cable).

 Soldering iron

 Solder

 Pliers/wire cutters

 Screwdriver (Crosspoint or Phillips)

 Electronic multimeter or circuit tester (if you have a multimeter, it will have an “ohms” setting — use this for circuit testing).

Cable Assembly

You assemble the cable as follows:
1. Take the wire with the 9-pin D connector at one end and cut off any connector at the opposite end.

2. Cut the outer sheathing off the trimmed end and expose the inner core of wires.

3. Strip the ends of the wires.

4. Using a multimeter, you need to determine which wires corresponds to the data in and data out and ground pin on the 9-pin connector. To do this, set the multimeter to “ohms” (the 20 ohms setting will do just fine). Attach one probe to the bare wire; wrap a length of paper clip around the other probe, and probe the holes in the connector. Try them in turn; you are looking for a reading of zero, indicating that you have the right wire for the pin. The pins are as follows:
■ Pin 2: Data out
■ Pin 3: Data in
■ Pin 5: Ground

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F IGURE: A multimeter makes it easy to trace what wire goes to which pin.

5. Trim back all the unneeded wires and cut the wires from pins 2, 3, and 5 to a length of approximately 1 inch (25 mm). Trim the sheath from these wires back about 1 ⁄ 4 of an inch (6 mm).

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F IGURE : Trimming back the sheathing

6. Now take a look at the pFranc eTrex connector. Notice that it has four pins. The pins are numbered 1, 2, 3, and 4, with pin number 1 being the pin furthest away from the cable. The pins are as follows:
■ Pin 1: Power supply (+)
■ Pin 2: RXD (data in)
■ Pin 3: TXD (data out)
■ Pin 4: GND (-)

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F IGURE: The pFranc connector

7. Time to begin assembly of the pFranc connector. The connector includes five parts:
■ Three plastic parts that make up the connector assembly
■ One metal screw
■ One strip of metal that has the four or eight pins attached to it (depending on the kit you receive).

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F IGURE : Metal strip with the pins

8. Carefully break off the pins (you only need three if you are making a data cable) from the sheet of metal by bending them off the metal strip. Take care and you will end up with four pins.

9. After breaking the pins free from the metal strip, bend them to 90 degrees.

10. Now it’s time to solder the wires to the pins. At this stage, it doesn’t matter which pins the wires are soldered to because you can rearrange them as necessary later.

After soldering, gently push each pin, one at a time, through the hole in the plastic piece with the large rectangle opening.

11. Now you are ready to place the pins in the proper position in the plastic holder (the base of the connector). The proper assembly is as follows:
■ The wire corresponding to pin 2 (data out on the 9-pin D connector) connects to pin 3 (data out) on the GPS connector.

■ The wire corresponding to pin 3 (data in on the 9-pin D connector) connects to pin 2 (data in) on the GPS connector.

■ The wire corresponding to pin 5 (ground on the 9-pin D connector) connects to pin 4 (ground) on the GPS connector.

12. A clever way to hold the pins in place while assembling the connector is to use a piece of wire (or a needle) through the loops of the pins to hold them in place.

13. Bring the two parts of the connector together and then place the plastic hood on the connector. Make sure that all the cables seat properly and there is no chance of short-circuiting. Then add the screw and close the connector.

14. Remove the pin, needle, or wire used to hold the pins in place and the connector is finished.

Testing

You should always test your cables before first use to ensure that there are no short circuits or bad connections. Use a multimeter to do this. Make sure that each pin on the GPS connector corresponds to the appropriate pin on the 9-pin connector. Also ensure there are no short circuits to any other pins.

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