Speed - the free speedometer

sportsfan12321

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Jul 20, 2008
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#1
Cool app, tested it in the car today, seems to be very accurate. One thing though...how does it work? I've turned 3G off and edge as well using an APN mod, but somehow it still is able to detect my speed? I'd assume it uses the built in accelerometer, but it doesn't make sense considering car's velocity is constant at times...
 

g33k1

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Sep 6, 2007
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San Antonio Tx
#2
Cool app, tested it in the car today, seems to be very accurate. One thing though...how does it work? I've turned 3G off and edge as well using an APN mod, but somehow it still is able to detect my speed? I'd assume it uses the built in accelerometer, but it doesn't make sense considering car's velocity is constant at times...
GPS I would assume
 

jpm

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Aug 5, 2007
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#3
It uses the iPhone GPS.
 

sportsfan12321

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Jul 20, 2008
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#4
I assumed the GPS used a data network to transfer info?

Otherwise wouldn't there be additional charges for using the GPS?
 

JoeT

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Dec 18, 2007
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Tampa, FL
#6
No! The GPS unit derives its latitude and longitude by triangulating based on signals received from multiple GPS satellites. The software then compares the latitude and longitudes and the time difference between them and calculates your speed. It has nothing to do with your data at all.

There is no charge to receive the GPS signals. You are already paying though your taxes. :)

http://en.wikipedia.org/wiki/Gps
 

jarofclay73

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Gold
Jun 23, 2008
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Honolulu, Hawaii
#7
I just dumped Speedbox in favor of Speed. Speedbox would never save my "mph" setting. I had to always change it every time I went into the app.
 

styfle

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Mar 31, 2008
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#8
so if you have the original iPhone, it wont work?
 

MaxCrack

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Sep 16, 2008
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#11
Simple Physics

According to the description it uses the GPS so no first gen phones.

There are a few that use the accelerometer. Based on a simple physics formula. The computer can figure it out thousands of times per second.

The best one of this type is Dynolicious. $13 is a lot for an iPhone app, though. But compared to a $200 stand alone unit it is a pretty good deal.

There is one that does perfectly fine for basic speed functions for around $5

==========Formula==========
Vf = Vi + At
Final Velocity = Initial Velocity + (Acceleration * Time)

If your Initial velocity is 30MPH and your acceleration is 0 over a given time then your final velocity is 30MPH.

How, exactly, the accelerometer knows what your rate of acceleration is, I do not know.