Winter 2009 Issue
Up in the Air
By Bill Brown,* WB8ELK
Photo A. Prototype board of the tracking beacon showing the USB converter, the Arduino Stamp, and the 434-MHz transmitter module.
No matter how many APRS trackers you may have
on a balloon flight, there is always a chance that they all will fail. In
that event, itís a good idea to have some backup. In those situations a
low-cost, low-power transmitter can really save the day. This circuit also
makes a great hidden-transmitter foxhunt device.
The brain behind the tracking transmitter is based on the Atmel AVR Mega168 microcontroller and is called the Arduino Stamp (SparkFun #DEV-08164). The Arduino is similar in appearance and size to the classic Parallax Basic Stamp but is programmable in the C language. This is a very powerful system and a great way to learn the basics of C programming. The Arduino system puts all the low-level items that make C programming tedious into the background and provides you with loads of high-level routines for performing A-to-D conversions, timing delays, serial communications, and digital I/O with very simple and easy-to-use commands. The best part of the system is that the Arduino development software is totally free (www.arduino.cc).
In addition, no expensive external programmer
is needed, since you can program the Arduino Stamp via a serial connection
(via the internal bootloader program in the microcontroller). Keep in mind
that the Arduino Stamp has logic level serial connections so you will have
to use a serial converter IC such as the MAX232 to interface to your
computer. However, SparkFun does carry a useful USB module that will
connect to the Arduino Stamp with just two serial lines and a common
ground. Itís called the Arduino Serial USB Board and is SparkFun item
#DEV-08165. The Arduino website shows how to hook up the USB converter
board to the Arduino Stamp on a prototype board (http://arduino.cc/en/Guide/ArduinoMini).
Photo A shows my prototyping setup of the complete tracking transmitter,
which includes the USB module to program the circuit. See figure 1 for the
tracking beacon schematic.
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