Under the Hood: Mobile star finder keeps it simple

With the "where and when" taken care of by GPS, the "which direction" relies on the earth's magnetic fields. One magnetoresistive sensor from Honeywell, the HMC1022, covers x and y. A second magnetoresistive chip (HMC1041Z), from the same company, provides angle of incline. Much like a compass with an added inclinometer, the two sensors finalize the overall (electronic) pointing vector into the planetarium stored in the database. Combining that information with the time and place on the earth's surface, the SkyScout can give you a report on what you are looking at.

For location vs. identification, all this works in reverse: The SkyScout guides the user to a selected feature in space by monitoring closure between the known target point and the pointing vector.

Dual-axis accelerometers supplied by Analog Devices join with the Honeywell sensors, with one accelerometer located on the board shown and a second located elsewhere in the system. We are guessing that the accelerometers are used either to determine rate of closure on a desired pointing direction for the "locate mode" or to help remove error through tracking of shake and vibration, but those theories are speculative. Readers' thoughts in this regard are welcome.

Other parts in the system are used for analog signal amplification, analog signal multiplexing and analog-to-digital conversion, but none is particularly complex or expensive. An AKM Semiconductor AK4366 audio codec interfaces the headphone jack to let the user hear descriptions of the objects being viewed. The Samsung processor is joined by 32 Mbytes of NAND flash, presumably holding both the system code and the celestial database, and 8 Mbytes of SDRAM for working memory.

The processor also handles all user interface, speech output and display driving for the 240 x 80-pixel monochrome LCD.

Despite the SkyScout's fairly amazing capabilities, the design relies fundamentally on low-cost sensors and ever-cheaper GPS location to get its bearings in three-dimensional space. Once that task is taken care of, a modest processing engine and an abundant collection of celestial data accomplish the rest.

The total cost of goods sold for the SkyScout accounts for a small fraction of the $399 retail price for the product, but don't let that keep you from buying it if you find the concept interesting. Celestron's premium here is the company's reward for clever design and a rich database of space.

Happy stargazing!

David Carey is president of Portelligent (www.teardown.com). The Austin, Texas, company produces teardown reports and related industry research on wireless, mobile and personal electronics.