APPROACHING THE FINAL FRONTIER
■ BY L. PAUL VERHAGE
This month, we cover the programming of the UltraLight’s Tiny Trak: the
APRS system responsible for transmitting regular position reports of the near
spacecraft. Unlike the PICAXE- 28 (which you program for each mission), you
program the Tiny Trak’s parameters just once. These parameters — set by the
Tiny Trak Configuration Editor — describe what position data the
Tiny Trak is to transmit and how often.
The Tiny Trak 3 used in the NearSpace UltraLight is an inexpensive Automatic Packet Reporting System
(APRS) transmitter. It receives input from an attached GPS
receiver and reformats the data into position reports that it
sends through amateur radio. The position reports are
essentially serial data transmitted as a series of two tones:
1,200 and 2,200 Hz. Over the radio, they sound like short
bursts of scratchy noise. The two GPS sentences used as
input to the Tiny Trak are the GPS receiver’s GGA and
RMC sentences. The position report transmitted by the
Tiny Trak therefore includes the time, latitude, longitude,
altitude, speed, and heading.
Byon Garrabrant N6BG developed the Byonics Tiny
Trak 3 as a simple-to-use APRS tracker that’s perfect for
high altitude balloons. Unlike many APRS trackers, this
one does not receive and decode APRS data; it only
transmits position reports. Parameters loaded into the Tiny
Trak by Byonic’s free Tiny Trak 3 Configuration Editor
describe to the tracker how it is to report its position and
under what conditions. These parameter settings are
stored in EEPROM so the Tiny Trak is ready to transmit
position reports upon powering up. Therefore, before
going any further, your first step is to download the Tiny
Trak Configuration software from www.byonics.com and
install it on your PC.
For your next step, you need to make a three-wire
programming cable. This cable swaps pins 2 and 3
between two female DB- 9 connectors and leaves pin 5
■ FIGURE 1. Since I make a lot of near space flight
computers, I built this durable Tiny Trak programming
cable. Its durability comes from the fact that the hollow
space inside of each DB- 9 jacket is filled with hot glue. Note
that there are only three wires between the two female
DB- 9 connectors. Pin 2 of one DB- 9 connects to pin 3 of the
other DB- 9 and pin 5 in each DB- 9 connects together.
connected between both DB-9s. Since this cable is
needed just once to program the Tiny Trak, don’t go to
elaborate lengths to make it; unless, of course, you plan to
program several flight computers or change the settings of
the Tiny Trak each time you fly a mission (Figure 1).
Now you’re ready to program the Tiny Trak.
Whenever you program the Tiny Trak, remove the
transmitter from the UltraLight because we don’t want the
Tiny Trak transmitting without an antenna. In fact, never
power-up the UltraLight before removing the transmitter or
attaching an antenna. Letting the radio transmit when no
antenna is attached is a sure way to damage the radio.
When the Tiny Trak 3 Configuration Editor starts, the
screen looks like Figure 2, sans the red circles and letters.
First, note that there are two tabs in the Editor:
Primary and Secondary. These two tabs permit the Tiny
Trak to operate under two different settings during a single
near space mission. The Tiny Trak settings under the
Primary tab are in effect while the PICAXE-28X output pin
5 is low; the Secondary settings are in effect when the
July 2011 69