Design Center:
Vehicle Position Logger
Since the U.S. military launched the first NAVSTAR global positioning system (GPS) satellite in 1978 and began full operation in 1995, GPS technology has improved dramatically and GPS has found its way into recreational vehicles, cellular phones, and shipping yards.
Today, the leading GPS receiver manufacturers offer a variety of chip- and board-level solutions for OEM's wanting to include GPS functionality in a product.
Figure 1. The Ashtech G8 OEM board.
This design example features Ashtech's low-cost G8 single-channel GPS receiver. Like many GPS receivers, the G8 outputs position, velocity, time, and other information using an asynchronous serial protocol (a TTL/CMOS-level version of RS-232).
Figure 2. Vehicle position logger block diagram.
Figure 2 shows a block diagram of the vehicle position logger. The AI2002A (DataBridge IC) captures serial data from the GPS receiver, recording to PC-compatible files on the target CompactFlash device. Using the message output feature, the AI2002A can be configured to automatically reset the G8 and set its output format format parameters.
Benefits
Low power consumption: When used with CompactFlash mass storage, the AI2002A's power consumption is very low (100-200 mW). The G8 consumes <700mW. And like the G8, the AI2002A draws power from a single 5V power supply. As a result, the circuit in this example operates 10 to 50 times longer on a set of batteries than a single-board or embedded PC circuit.
Stability and quick startup: The DataBridge-based circuit in this example is not susceptible to system crashes, long boot delays, and device driver conflicts. On powerup, the AI-2002A begins capturing and recording data within one or two seconds.
Short development cycle: Because the AI2002A handles all aspects of data capture, file system, and mass storage I/O, custom firmware development is unnecessary. RTOS and PC-based systems require in-house software expertise, careful programming, and licensing and royalty fees. If the circuit in this example is implemented using the SDR-OEM, even circuit board layout is unnecessary!
More Ideas
While the AI2002A in this example could be factory-configured to record GPS data, the designer may wish to add a RS-232 level translators connected to the AI-2002A's configuration serial port, allowing the user access to recording parameters, file transfer, and output message configuration using terminal software on the PC.
The AI2002A could be used to log data in parallel with a radio modem or land line in some applications; the radio modem provides real-time access to position, velocity, and/or time, while the CompactFlash card can be used to retrieve archived data.
Conclusion
OEM GPS receivers and the DataBridge IC are valuable tools for getting products to market quickly. The DataBridge IC makes data storage using CompactFlash and other industry-standard storage media a snap. The convenience of a PC-compatible file system makes integration with PC software simple. The AI2002A's low power consumption, small footprint, and dependability makes it the perfect solution for logging GPS data.
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