Why 2 accelerometers?

Al Johnson openmoko at mazikeen.demon.co.uk
Fri Sep 18 18:18:14 CEST 2009

On Friday 18 September 2009, RANJAN wrote:
> On Fri, Sep 18, 2009 at 8:35 PM, Al Johnson
> <openmoko at mazikeen.demon.co.uk>wrote:
> > On Friday 18 September 2009, RANJAN wrote:
> > > Hi,
> > >
> > > I was wondering why FR has two accelerometers.They could have one 3
> > > axis accelerometer and a single angular rate gyro.How is a combination
> > > for 2 accelerometers more useful than one 3 axis accelerometer and a
> > > gyro?
> >
> > Or, better, use a 3-axis magnetometer instead of a gyro.
> >
> > At the time the FR was designed, gyros were significantly more expensive
> > and
> > less available than accelerometers, and magnetometers were large and even
> > more
> > expensive. Spaced accelerometers sounded like a good way of getting most
> > of the way there while still being affordable. In practice it doesn't
> > work so well. In the meantime gyro and magnetometer prices have tumbled.
> I think when FR was designed the Gyros costed around USD 17 .Is there a
> next version of Openmoko phone being designed?

Openmoko are designing something that we don't know the details of, but that 
is supposed not to be a phone.

The gta02-core project is designing a phone, but this is more about the 
community development process and tools than the design itself. The aim is to 
produce a handful of boards, and if they're lucky they might even work.

There's a project to add a magnetometer to existing FRs using a little PCB 
above the SIM.

There's also the Flow which is fairly open and potentially fully featured, but 
rather expensive.

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