Nuts and Volts - December 2010

www.nutsvolts.com/index.php?/magazine/article/december2010_Grand

mechanism (that held the lifejacket). Zoz modified some of the control scripts for the MicroPilot system to direct the airplane to the desired dropzone with pinpoint accuracy. This system emulates practices by the US Coast Guard in which rescue equipment, food, or other payload is manually dispensed from an airplane flying over the person or vessel in distress.

The two systems were disparate efforts going on in parallel, but they both relied on a critical piece of information — a distress signal and location coordinates from the person in the water. Both systems required the swimmer to wear a small, battery-powered wristband transmitter that — when enabled by a button — would transmit his GPS coordinates to the receiving base station (Figure 3). Those coordinates — along with additional data such as wind speed, wind direction, and distance to the target — would be processed by the cannon or UAV control system, and a rescue attempt would commence.

This system received the GPS transmissions sent from the wristband and processed them accordingly.

This article details the wristband GPS transmitter used for both systems. While the episode as a whole was extremely complicated, this piece is very simple. It requires minimal hardware and firmware, and is something you'll be able to quickly put together and incorporate into your own location-tracking projects.

If you want a complete look into the Flying Lifeguard episode, all technical documentation I created for the build, including schematics, source code, and

Figure 3. Base station circuitry built on a Parallax Professional development notes is available on my website at www.grandideastudio.com/portfolio/pt-flying-lifeguard/.

The Hardware

The wristband GPS transmitter's core hardware components are a BASIC Stamp II, Parallax GPS receiver module, and AeroComm (now Laird Technologies) AC4490-200A 900 MHz RF transceiver module which Figure 4. Schematic.