The Global Positioning System (GPS) has to be one of the coolest technologies ever conceived of by humans. Although GPS has become commonplace because of smartphones it is still an amazingly advanced technology. However, for only a few dollars it’s possible to incorporate GPS into your new electronic product.
Introduction to GPS
GPS was developed by the US military in the late 70’s. The system consists of a minimum of 24 satellites in high orbit around the Earth. These satellites travel at nearly 9,000 miles per hour and orbit at an altitude of 12,000 miles. Each satellite carries an atomic clock with an accuracy of about 1 nanosecond. The satellites are distributed so that there is a line of sight to a minimum of 4 satellites from anywhere on Earth’s surface. The GPS receiver on the ground receives timing and location data from these satellites on a 1.575 GHz radio carrier signal.The GPS receiver is able to then determine the distance to each satellite by timing how long it takes for the radio waves, which travel at light speed, to arrive at the receiver. By knowing the exact distance and location (encoded in the signal) of at least three satellites the receiver’s microprocessor is able to trilaterate its location. The fourth satellite is required as a redundant check and to provide timing corrections.
The term GPS actually refers only to the use of the satellite network operated by the United States. However, there are other navigation systems in operation such as Russia’s GLONASS network, China’s BeiDou network, Europe’s soon to be Galileo network, and Japan’s QZSS network. The term Global Navigation Satellite System (GNSS) is the more generic term that refers to any of the above systems.
Implementation can be split into three types of solutions: full modules with an antenna, chip modules without an antenna, and discrete chip solutions. Table 1 below summarizes the advantages and disadvantages of each type of solution.
Table 1 – Comparison of GPS solution types
I always advise entrepreneurs to first focus on minimizing their development risks and costs even if that means a solution that doesn’t leave much, if any, profit. It is better to worry about maximizing profit after you’ve had some real market success.
All of these solutions interface with your product’s primary microcontroller via a serial UART interface. In most cases, they will output GPS coordinates in a standardized format known as NMEA (National Marine Electronics Association).
Full Module Solution
The simplest way to implement GPS is by using a full module that includes either a built-in antenna, or a connector for an external antenna. See Table 2 below for a comparison of four popular full GPS modules available.
|Full Module||GNSS||Discrete Chip||Sensitivity||Size (mm)|
|uBlox CAM-M8||GPS, GLONASS, QZSS, BeiDou||uBlox||-167 dBm||14 x 10 x 2|
|AdaFruit Ultimate GPS||GPS, QZSS||MT3339||-165 dBm||35 x 26 x 7|
|Telit SE868-A||GPS, GLONASS, QZSS, Galileo||SiRF Star V||-163 dBm||11 x 11 x 6|
|SparkFun GPS Module||GPS||Copernicus II||-160 dBm||28 x 32 x 4|
Table 2 – Comparison of full GPS modules (ordered from highest sensitivity to lowest)
Full modules offer the lowest development cost but the highest unit cost so they are usually only appropriate for early testing (or for DYI projects). The best solution for bringing a new product to market is to use a chip module.
Figure 1 – Adafruit Ultimate GPS full module with antenna connector
Chip Module Solutions
A chip module solution typically does not include a built-in antenna and usually requires at least a few external components. However, chip modules are much less risky than a discrete chip solution. See Table 3 for a comparison of eight chip modules currently available.