Most people are familiar with GPS: the Global Positioning System run by the United States Government. It allows a GPS receiver to locate its position anywhere on the planet by analysing signals received from a series of orbiting satellites. (For a more detailed explanation of GPS, see the separate panel in this article).

Quite a number of hand-held receivers are available at reasonable prices. These show your position as a latitude and longitude on an LCD readout. They’re ideal for bushwalkers, hikers, etc – and fishermen love them because they can get back to that secret spot – exactly!

Some of the higher end models allow the position to be displayed on a map along with other numerous features.

But what if you’d like to interface a GPS directly to your PC or laptop?

Most of the cheaper hand-held units don’t support an external interface at all – or if they do, it is an expensive option.

There is also the question of battery life (which is normally quite short anyway). If you’d like extended logging of data, you’re up for yet another add-on for external power, not to mention an external antenna if it’s not convenient to mount the entire unit in a spot that gives good coverage.

As you can imagine the task of tracking and analysing signals received from the up-to-12 satellites that can be in view at a single time is quite a complex task.

Fortunately quite a number of OEM (original equipment manufacturer) GPS modules are available that perform most of the real work and interfacing one of these modules to a PC or other serial device is quite easy.

This article describes constructing such a unit at a cost considerably less than using a hand-held unit and gives some pointers on getting some usable data out of the GPS module once it’s built.