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Is there a device which acts like an accelerometer but only measures absolute velocity? I could integrate the accelerometer's output but errors quickly accumulate and cause problems. Preferably the device is available in a MEMS based chip and is low cost. I could use a GPS device (and am currently, with success), but this is expensive, bulky, and requires a GPS link, which is not available in all circumstances.

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How would such a thing even work? It needs an external reference of some sort, like GPS or other positioning system. – endolith Apr 14 '11 at 1:43
@endolith Simple, its almost like measuring voltage with a single probe (no ground reference). Wait, not so simple :-) – Kellenjb Apr 14 '11 at 2:41
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I presume you mean without mechanical contact with a surface such as a trundle wheel and rotary encoder? Or a surface with stripes on it? That gives me a thought, do you mean like a laser mouse? – Martin Apr 14 '11 at 9:13
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Perhaps if you describe your application, there might be some usable solution. As others clearly pointed out, you can't simply measure velocity in a self-contained manner. – Toybuilder Apr 14 '11 at 12:16

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There is no such thing as absolute velocity; velocity is always relative to something. Velocity cannot be measured internally to a chip (as can acceleration). You must have external input, such as radio references a la GPS or sensors detecting changes in other phenomena external to the chip and its vehicle.

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As has already been said, there is no such thing as absolute velocity, however STM make a 3D motion sensing chipset (iNEMO). Details of the evaluation kit here

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