One recent contract design I did for a military contract placed an Ecompass on the main board of a portable GPS device.True, that multiple subsequent GPS fixes will provide a compass heading, the need was for a foot soldier who may be hunkered down in a foxhole, and needed direction.From the designer's perspective, many things can affect the Ecompass performance as Jon pointed out: shields, capacitors, and any Fe based components.
But two surprises were the screws and the Stainless steel shields. First, the screws were expected to wreak havoc with the Ecompass, but careful placement of the SMD to be equidistant between two screws proved sufficient .Test readings still came thru perfectly.
The second surprise was the SS shields, and we went to great lengths to requalify new, NiAg shields as engineered replacements.Halfway into the effort to requalify NiAg, one of the techs put a white-board magnet on the rev 1 stainless steel shield being phased out.It didn't stick.Foolishly, I took for granted without actually checking the metallurgical properties of the grade of SS shields, that they in fact did not possess any iron and did not affect the Ecompass performance any differently that the newer Nickel Silver shields.Didn't do my homework and it resulted in a lot of extra work for no reason.
Thanks for this @Jon. With the increased availability of compact, integrated sensors and low-power computing, I expect the boom into "sensor fusion" is just starting. I'm delighted to read that Freescale did all of the difficult calibration analysis and created an on-board algorithm. The application note you linked even includes the source code for the calibration algorithm they developed. Kudos to Freescale for making their code open so it can be reviewed, modified, improved, and adapted by the sensor community. I hope they can be an example for other instrumentation manufacturers.
Rotating the chip itself in relation to hard/soft iron can dramatically improve performance. We have a design which uses a compass in close proximity to a brushless motor. It isn't intended to provide a true heading, but does monitor rotation.
Because semiconductor manufacturers make complicated devices and want designers to use them, they create development tools and provide source code that illustrates how to use these devices. I'd say almost all MCU and programmable-sensor companies offer hardware and software to help engineers and product designers get off to a good start. In most cases, open-source code provides a way to start with a core of working software. Of course, the code might run optimally only on the MCU-maker's chips.
A middle school team from Rochester, Mich., has again nabbed the grand prize in the annual international Future City Competition, which drew students from 37 regions of the United States, as well as from England and China.
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