Nuts and Volts - January 2012

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)