affordable lap timer

wstar

On the GPS: The 818XT is switchable between 10Hz mode (with GPS only, no differential), and a programmable 1-5Hz mode that uses differential GPS (more accurate). From the forums for various lap timer software on android, it seems like the 5Hz D-GPS mode is actually better (more accurate, faster fixes, and still you're getting 5 position updates per second, which the software can extrapolate movement curves between).

OBD-II loggers vary a lot, it's kind of a murky area. With the PLX Kiwi and my phone, I get somewhere around 4Hz update rate most of the time. So for instance it will rarely catch the exact peak RPM just before a shift, but it's "close enough" for data analysis. Software like aLapRecorder logs all the inputs (phone G-sensors, OBD-II data feed, GPS data feed) and then reformats it into a combined data output file for rendering software (e.g. a single CSV file for RaceRender), which in turn probably does a little of its own smoothing and/or interpolation.

It doesn't really matter if OBD-II and GPS data line up at the same update frequency rate or not, or shouldn't with quality software on the other end interpolating them as approximating smooth value curves.

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