There is no need for a loop after soldering since the large
diameter hole in the PCB blocks most of the strain on the
battery snap from reaching the soldered connection. Now,
repeat this for the two wires of the GPS cable. These wires
are about a foot long and have 1/4” of insulation stripped
from both ends. Start by soldering one end of each wire
to the PCB with the same method used for the battery
snap. The other end of each wire solders to a solder cup
in the DB- 9. In Figure 4, placement diagram above, each
wire is labeled with its correct solder cup — 2 and 5. Now,
the GPS simulator is ready for its first test.
TESTING THE GPS SIMULATOR
■ FIGURE 3. Solder the components to the PCB as
indicated in this placement diagram.
place the spacers between the wings of the DB- 9 and the
PCB, and bolt the DB- 9 to the PCB with the 4-40
hardware. When soldering the electrolytic capacitor,
voltage regulator, and LEDs, watch their polarities.
All that remains to solder are the wires for the battery
snap and the GPS cable. The battery snap solders to the
two solder pads at the top of the PCB diagram in Figure
3. The diagram shows the battery snap leads in red and
black to match those in the battery snap. The other two
wires (one black and one white) for the GPS cable appear
at the bottom of the placement diagram. The other ends
of these wires terminate in pins 2 and 5 of the DB- 9
connector with the solder cups.
The wires in the battery snap and the GPS cable are
strain relieved to the PCB so they will not break off from
everyday use. Solder the nine volt battery snap first. Strip
1/4” of insulation from the ends of the wires (if they are
not already stripped) and pass them through the large
diameter strain-relief holes. Then, bend them over and
insert the bare ends into their correct solder pads as
shown in Figure 4.
I find leaving a small loop in the wires helps press the
bare ends into the solder pad. After soldering both leads
of the battery snap, trim the wires and pull the wires tight.
The first test locates any electrical shorts in power.
Use a DDM set for continuity and check between the
positive and negative terminals in the battery snap. The
meter should not ring. If it does, check the underside of
the PCB for any solder shorting traces. Next, test that the
proper voltage appears on the PCB. Set the DMM for
voltage and plug a nine volt battery into the snap. Measure
between pins 5 and 14 on the IC socket and verify that
relative to pin 5, there is positive five volts (give or take
1/2 volt) on pin 14. Remove the battery snap and install the
PICAXE-18M2. The last test is a test of communications.
Start up the PICAXE Editor and set it for the PICAXE-
18M2. Type the following program into the editor:
Plug the nine volt battery back into the battery snap
and download this program. Verify that the editor
programmed the PICAXE and that the Debug window has
one update. At this point, you’re ready to download the
GPS simulator code, which you’ll find at the article link.
After downloading this code into the PICAXE, start up the
terminal program in the editor by clicking the F8 key. Note
that the Lock LED is red (no position lock) and the Launch
LED is off (balloon on the ground). Unplug the programming
cable from the DB- 9 on the GPS simulator PCB and plug it
into the DB- 9 on the end of the GPS cable. The PICAXE
terminal will now show data as in Figure 5.
If every test has been successful, then complete the
last step in the construction of the GPS simulator. Squirt
hot glue around the solder cups in the DB- 9 of the GPS
cable. Then, fill one half of the plastic DB- 9 hood with hot
glue and lay the female DB- 9 into the hood. Top off any
low spots with hot glue and then fill the other plastic
DB- 9 hood with hot glue. Close the second hood and
bolt the entire assembly together. Finish by back-filling
the DB- 9 hood with additional hot glue. When back-filling the DB- 9 hood, squirt glue into the opening in the
back of the hood until the hot glue is about to run out.
■ FIGURE 4. This image shows the insulated wire
passing through the larger strain relief hole on the right.
It then bends over, and the stripped end of the wire
passes through the smaller solder hole to be soldered.