[android-discuss] Re: Simulating a compass with bearing and accellerometer? - efon...@gmail.com - com.googlegroups.android-discuss

14 messages in com.googlegroups.android-discuss[android-discuss] Re: Simulating a co...

From	Sent On	Attachments
efon...@gmail.com	15 May 2008 20:22
efon...@gmail.com	17 May 2008 04:48
James	18 May 2008 05:47
efon...@gmail.com	19 May 2008 04:32
Alex Pisarev	19 May 2008 05:51
efon...@gmail.com	19 May 2008 10:13
Peli	20 May 2008 05:21
James	20 May 2008 05:47
James	20 May 2008 06:20
efon...@gmail.com	20 May 2008 13:27
efon...@gmail.com	20 May 2008 15:50
efon...@gmail.com	21 May 2008 04:42
efon...@gmail.com	21 May 2008 06:11
efon...@gmail.com	21 May 2008 15:09

Subject:	[android-discuss] Re: Simulating a compass with bearing and accellerometer?
From:	efon...@gmail.com (efon...@gmail.com)
Date:	05/21/2008 03:09:26 PM
List:	com.googlegroups.android-discuss

A card compass floating in a liquid sphere with pick ups on the wall meets all the criteria.

On May 21, 8:11 am, "efon...@gmail.com" <efon...@gmail.com> wrote:

52 card pick up outside, when the wind is blowing 20 knots, doesn't sound so good.

Inside a cell phone the B fields might be like 20 knots and swirling...

1. Only measure when quiet ie measure really fast after shutting off all things that mess up the reading. 2. Shield the sensor 3. Choose a goo time constant such that persistent fields are measured but hi frequency stuff is rejected - design a low pass filter characteristic in the mechanical implementation of the sensor specifically for reliable operation inside cell phones. 4. Just use spaced accelerometers and forget magnetism - work in g's

Anyway, good enough does not have to be expensive. It is a will function.

On May 21, 6:42 am, "efon...@gmail.com" <efon...@gmail.com> wrote:

James,

It took me a while to understand what you were saying.

I think it would work and is incrementally free except for that calibration step.

There are concerns about effects of building when one is not in an open field, and the hard edges they have.

…A pulsed simulated MEMS birds eye might work.

http://www.npr.org/templates/story/story.php?storyId=90186088

It feels like $1.25 to me, because it is not a dry process. (note: a 2- D version that does only one axis might be a lot easier to make the first time!) The idea is:

1) create a [hemi-spherical] cavity with a tossing mechanism on the surface. Maybe an LED or a mechanical trampoline or an electro-magnet or just electrodes. 2) add sensors/junctions/dopants on the surface 3) put in simulated birds eye goop. The viscosity of the suspension goop and even the need for goop are TBD having to do with toss and catch time constants of the molecule you are tossing. I would try filling it with dust first, maybe iron filings (ferrite dust is less sticky) - do you even need magic birds eye chemicals and the associated energy cycle? It might be that need goes hand in hand with the suspension goop?

Anyway, the compass works in a pulsed way by tossing the magnetically active/polar stuff off the wall and then sensing how it lands. Toss/ Sense, Toss/Sense....

The suspension goop might still be required to damp out the history of the toss before the landing occurs.

Goopless it is 80 cents, with goop it is $1.25.

Either way you can put it in an affordable handset and it will earn its keep in less than a month.

Adding your sensor fusion thought from a while ago and Peli's picture of an accelerometer as an indicator of 'which edge of the phone has the water sloshed to?' you actually get something that does work.

You know the direction of g from the accelerometer. Toss the magnetic dust up in a sphere and when it lands it will not land aligned exactly with the g vector. It will be displaced toward magnetic north. There an inexpensive compass that works good enough for our purposes. for $1.05 and $1.50.

So everybody gets phones that are perpetually playing 52 card pickup.

Now that that is solved, it is time to focus on compelling software ;-)

On May 20, 8:21 am, James <jame...@yahoo.com> wrote:

efontana,

If an existing cell phone does not have a sensor you want, then the only alternatives are to make the best use of what you have available, or not to provide the function at all.

By using the variable signal profiling, it is useful for when a dedicated compass sensor is not available in the cell phone. The variability due to a persons body, phone orientation, obstructions, transponder location relative to cell phone, ... all have to be taken into consideration to make a useful product.

One potentially useful scenario might be:

Instructions for using compass.

"Walk in a straight line in the direction the top of the cell phone is pointing; choose a target to walk toward and hold the cell phone flat like you would any mechanical compass. The cell phone will beep when you arrive at the calibration position."

"After hearing the beep, rotate about your position smoothly and slowly (4 seconds, 1 second and 1 beep for each 90 degrees), until you return to face your starting position. The display will automatically display the compass bearing around this position."

"If you move more than 15 feet from this position, the compass bearing will be removed from the display until Calibration is done for a new position. This prevents the user from using old data."

This would be done every time a person wanted a compass bearing.

At this one position, they could rotate back and forth and get compass bearing information. When the GPS sensed any new position, the Compass would replace the compass readout with "Perform Calibration".

They would have to repeat calibration every time they wanted a compass bearing unless higher level algorithms are running in the background while the user is walking. Updating lookup table(s) with information to derive similar data from moment to moment.

Again, this scenario is only useful if a compass sensor is not available in the cell phone. Which is almost all cell phones made today.

But I agree, if a compound MEMS chip (with Mag sensor) were incorporated in cell phones then this sensor fusion option would be unnecessary.

James

On May 19, 5:33 am, "efon...@gmail.com" <efon...@gmail.com> wrote:

Hi James,

This is helpful. Thank you. It is good to know someone is thinking about this. After reading the IEEE abstract, a little clarification on use is always helpful.

Our applications are eyes free, because the phone should not be competing for those revenue generating resources. So use will happen with the phone stored on the person’s body, say, in a shirt pocket, held to the person's ear, or on their belt. The compass needs to work no matter how the phone is oriented. The IEEE abstract seemed unclear on how it would work in a handheld device. It would be great for cars, though. With the two accelerometers, there is a calibration routine where a person wears the phone normally and walks in one direction. 10 ft should be enough to get enough calibration to be useful. It can recalibrate in the background and alarm or adjust ...

Sensor Fusion is a new word for me. Differential sensors of finite resolution have been around for a long time. Consider the roach, or any bug with antennae. They sample air at distant points allowing the organism to select a direction. The longer the antennae, the smaller the gradient the organism can detect with sensors of a fixed resolution. Long antennae help folks figure out what is going on. Sampling acceleration at distant points is going to give you better information on angular velocity and acceleration (how fast you are spinning) than using a single sensor in the same way.

Thank you for pointing out that radio field interaction can provide information... since a human body can influence that, it is probably good to not rely on that method. Two sensors a fixed distance apart should require little attention and provide good results across many devices once it is engineered.

My job is to show why it is worthwhile to spend that dollar for pedestrians who don’t read maps. Android has the tools to do that, even in today’s SDK.

On May 18, 7:48 am, James <jame...@yahoo.com> wrote:

A MEMS chip can be a collection of sensors (temperature, accelerometer (x,y,z), atmospheric pressure, Hall effect sensor (compass), ...) all built into the same chip. In mass production the chip could be relatively inexpensive.

http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/20/35967/017046....

However, an Android shortcut would be to use the GPS sensor and your relative direction of travel to produce a compass bearing over 100 feet of uniform travel. For each model of cell phone the antenna sensitivity changes as you rotate the cell phone about a point. This could potentially be tied in with relative position movement to estimate a compass bearing about a point.

But as I said, the lookup table would be different for each model of cell phone.

This type of engineering where you take two sensors with low resolution to combine their results to provide greater resolution is called "Sensor Fusion".

Basically a cell phone antenna signal does NOT have the same signal profile when you rotate left versus rotate right. This can be capitalized upon to determine the relative bearing of which the compass is facing. Coupled with the cell phone GPS the relative bearing can be referenced to the true bearing. A lookup table can provide a correction factor and thereby produce Magnetic Bearing; vis vi Compass.

James Dunn Table of Contents - Similar Insights related to technology applicationshttp://blog.360.yahoo.com/jamesbdunn?p=207

On May 15, 9:23 pm, "efon...@gmail.com" <efon...@gmail.com> wrote:

I have no idea how much a cell phone with a compass costs. I don't see why it would be expensive if there were enough of a market to micro machine it like all those tiny mirrors. > Who knows these answers?

Thanks, Ed- Hide quoted text -

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