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David Ashton
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Re: Bosch MEMS sensor - air pressure and SI units
David Ashton   2/13/2014 5:15:10 PM
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@DrQuine....I didn't know about buildings being pressurised.  As you say there are ways round this but the easiest thing is probably to find an elevator and see what floor you are on :-)

DrQuine
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Re: Bosch MEMS sensor - air pressure and SI units
DrQuine   2/13/2014 4:58:32 PM
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Thanks for the "QNH" aviation explanation.  Certainly the same approach could work for SmartPhones: the GPS would provide a location and the nearest reference barometer could provide the correction factor.  The one remaining issue would be the pressure differential inside the building.  Many buildings run at positive pressure which would cause the "altimeter" to read a lower floor level than it should (denser air). Perhaps a simpler approach would be for the GPS to detect entry into the building perimeter, use the indoor ground level air pressure as the barometric pressure reference. It could then compute floor levels by the associated pressure reductions as the air pressure reduced with increasing altitude.

Susan Rambo
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Re: Smart"phone" has now become a misnomer
Susan Rambo   2/13/2014 6:18:52 AM
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Hi prabhakar_deosthali: Yes it's like the smartphone is really a tricorder and communicator put into one. Even Star Trek didn't think of that one.

Susan Rambo
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Re: Bosch MEMS sensor - air pressure and SI units
Susan Rambo   2/13/2014 6:14:02 AM
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Yikes. Sounds like altimeter designers are under a lot of pressure. (Bad pun I know.)

Susan Rambo
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Re: Bosch MEMS sensor - air pressure and SI units
Susan Rambo   2/13/2014 6:07:36 AM
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Thanks. Yes I was disappointed when I found out an altimeter is really just a barometer with more math. (In other words, you subtract the local weather conditions.) Once I wanted a fancy watch with an altimeter on it for hiking but when I found out the altimeter was just a barometer, I decided it was just a toy (for my purposes). An altimeter wasn't going to keep me from getting lost.

David Ashton
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Re: Bosch MEMS sensor - air pressure and SI units
David Ashton   2/12/2014 6:45:26 PM
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The same problem applies to aircraft altimeters - the pilot gets a "QNH" (I think) figure which is the sea level pressure at his location, puts it in and the altimeter is accurate.   So all you need is some way of (preferably automatically) telling the phone the QNH and it should be accurate...

DrQuine
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CEO
Re: Bosch MEMS sensor - air pressure and SI units
DrQuine   2/12/2014 6:04:52 PM
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The sensor claims to be able to read your barometric pressure altitude within 3 feet (which would define the floor of a building). The challenge is that is needs to adjust for weather related pressure changes which could cause the readings to be off by 30 floors...

DrQuine
User Rank
CEO
Re: Temperature and Humdity Sensor in a Smartphone
DrQuine   2/12/2014 6:01:15 PM
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Sounds like we need remote bluetooth temperature sensors for the iPhone - we care about the temperature outdoors as we drive, not in our pocket where the phone is resting. Maybe some of our car sensors can grant read-only access to our SmartPhones.

Susan Rambo
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Blogger
Re: Bosch MEMS sensor - air pressure and SI units
Susan Rambo   2/12/2014 11:56:27 AM
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@DrQuine: "It also provides an interesting object lesson in atmospheric pressure in SI units."  Interesting! Thanks Dr. Quine. So what you're saying is the Bosch MEMS sensor can measure such small pressure changes that it can tell if you're on the 4th floor or the 30th floor and not be affected by general pressure changes in or outside building (weather, HVAC)?

Susan Rambo
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Blogger
Re: Temperature and Humdity Sensor in a Smartphone
Susan Rambo   2/12/2014 11:44:19 AM
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That's a good point. Users of smartphones will become more savvy to all the sensors and know how to get a more accurate reading.

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