# idea for Neo 2nd generation: Accelerometer

Tim Newsom cephdon at gmail.com
Fri Jan 26 16:50:58 CET 2007

```On Thu, 25 Jan 2007 23:12, Jeff Andros wrote:
> as I understand it, you can get more value out of the accellerometer
> than that
>
> in the simplest case, we know a gps can be off by a certain percent.
> say you leave the phone still for a long time, you could average the
> error and get more precise over time (yeah, there'll be some skew...
> but we can trust the law of averages to help us out some)
>
> now, say you were aware of the motion of the device, you could still
> account for that motion in the averaging process (A-meter says I've
> gone 2 feet, gps says I've gone 3... pretty safe to say I'm between
> those)
>
> one of the real weaknesses of the accellerometer(INS) are long-term
> integration errors, and the biggest weakness of gps is short term
> precision... put the two together and they complement each other REALLY
> well.  our (US) military has been using this combination for years with
> really great(horrible?) results... it'd be great to put this to a
> peaceful use as well
> --
> Jeff
> O|||||||O

We also need to take into account that accelerometers measure
acceleration.  If you accelerating or decelerating it will be able to
tell you the magnitude of the force and you can time the duration to
find the distance traveled.  However, suppose that you are moving at a
constant velocity,  the accelerometer will measure 0 (zero)
acceleration.  Most true vehicle dead reckoning systems also include a
sensor for the vehicle speed, which in combination with gps can provide
you with something the accelerometer can't.  The ability to know how far
you have traveled at a constant or accelerating speed.

Anyway, since attaching a sensor to the car may not be possible its a
moot point.  Just thought I would add a few more cents in.

As a side note... In the US and probably other countries there is a
standard for the interface to the car computer.  From that interface you
can get the vehicle speed and diagnostic information about how the
engine is running.  It might be interesting to have some kind of
bluetooth car interface to obtain that information and display it for
you while you are in your car.  Anyone ever heard of anything like
that?

--Tim

```