The microprocessor does everything in the navigation system except for activities that require specialized, dedicated electronic circuitry. For a unit based on the global positioning system (GPS), there are specialized circuits to detect and time microwave signals emitted by an array of earth-orbiting satellites and specialized circuits to operate a display and a sound system, but that’s about it. Everything else is done by one or more microprocessors.
Microprocessors now play a dominant role in most electronic devices because microprocessors allow their sophisticated circuits to be reused endlessly for many different purposes. Prior to the microprocessor revolution, electronic devices had to implement separate circuitry for each and every task or process. Nothing could be reused or reassigned, even if it wasn’t doing anything most of the time. With microprocessors, reuse and reassignment is easy and leads to enormous improvements in circuit efficiency. Devices that were once huge, expensive, and power-hungry can now be reduced to a small printed circuit board featuring a tiny microprocessor and a handful of dedicated circuits that are responsible for conveying information to and from that microprocessor.
A navigation system is a fine example of this shift to microprocessor-centric electronics. Earlier navigation systems, such as the instrument navigation systems (VOR) used by aircraft, involved a lot of specialized electronics and still only provided the pilot with information about the plane’s angle relative to a ground-based transmitter. The pilot needed at least two of these systems and a set of good maps to figure out where the plane was.
A modern, GPS-based navigation system simply hands the pilot or driver complete information about where the plane or car is located. It does this using specialized input circuitry and specialized but very ordinary computer output circuitry (a display and sound system). Everything else is done by the microprocessor.
The input circuitry in a GPS receiver is interesting. The global positioning system consists of an array of earth-orbiting satellites that use microwaves to announce their locations and emit timing pulses. The navigation system’s circuitry detects those microwaves, determines the satellites locations, and uses the timing pulses to measure the distance to each satellite it can detect. Since microwaves travel at just under the speed of light through earth’s atmosphere, knowing how long it takes for a pulse to travel from a satellite to the navigation system is equivalent to measuring the distance separating those two objects.
Once the navigation system’s specialized electronics has received information about the satellites’ locations and measured the travel times of their pulses, that information is passed along to the microprocessor. The microprocessor does everything else. It converts pulse travel times into distances, uses those distances to triangulate the navigation system’s location relative to the satellites, looks up information about that location in its stored maps, and displays relevant information to the pilot or driver. Easy peasy.
The specialized circuitry necessary to receive location and timing information from the GPS satellites was once complicated and expensive. But the desire to put such circuitry in every cellphone propelled amazing miniaturization. The GPS receivers now built into cellphones are tiny and inexpensive, and they include their own microprocessors. Part of the microprocessor revolution has been that many devices contain entire networks of microprocessors rather than just one centralized microprocessor. Having many microprocessors that communicate via a network can save a lot of specialized wiring and it turns out that wires can be more expensive than microprocessors. Cars and planes now have communications networks that allow their many microprocessors to exchange information and control components with only a handful of wires.