www.nutsvolts.com/index.php?/magazine/article/january2012_NearSpace
NEAR SPACE
■ FIGURE 2. Schematic.
GPS sentences once every second and the Lock LED turns
green. If the GPS lock is switched off after the balloon is
already in flight, the simulator keeps track of its virtual
position while the GPS simulator reports no position lock.
The balloon is virtually launched by pressing the
Launch button. Until then, the GPS position doesn’t
change and the Status LED is off. The Status LED is green
during ascent, toggles between red and green during float,
is red during descent, and is off on the ground. The
simulator’s programming port is a female DB- 9 soldered to
the PCB, and it does double duty by sending position
reports to a PC. The GPS output is through a second
female DB- 9 attached to the end of a two-wire cable.
Attaching it to a cable makes it easier to plug the GPS
simulator into a GPS tracker.
MAKING THE GPS SIMULATOR
VERSION 2.0
The Parts List shows the components needed to make
the GPS simulator, version 2.0. Many of them you’ll
already find in your parts bin.
All holes in the PCB (printed circuit board) are 0.032”,
except for the four holes used for strain relief. These holes
(circled in Figure 3) are drilled larger at around 0.050” in
diameter. After drilling the PCB, begin by soldering the
resistors. Follow with the capacitor and then the IC socket.
Do not insert the PICAXE-18M2 at this point. Next, solder
the LP2950 voltage regulator and the two miniature
momentary pushbutton switches. The Lock and Launch
LEDs are bi-color LEDs, and the LED near the voltage
regulator is a standard single color LED. Solder all nine of
the female DB- 9 connector pins to the PCB. Afterwards,
Parts List
• 18-pin DIP socket, 300 mils wide
• PICAXE-18M2
• 4K7, 1/4W resistor ( 2)
• 1K, 1/4W resistor ( 3)
• 22K, 1/4W resistor
• 10K, 1/4W resistor
• 22 µF electrolytic capacitor, 100 mil lead spacing
• LP2950 five-volt low drop-out voltage regulator
• LED
• Bi-color T1¾ LED ( 2)
• Tactile normally-off pushbutton switch ( 2)
• Nine volt battery snap
• DB- 9 female connector, PCB pins
• DB- 9 female, solder cups
• DB- 9 hood kit
• 4-40 bolts, 1/2" long ( 2)
• 4-40 nylocks ( 2)
• 4-40 plastic or aluminum spacers, 0.2" long ( 2)
• Wire, 24 AWG, two feet long
• PCB (use the pattern included in the article downloads)
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