Whatever happened to doppler speedometers mounted under the car ? I
thought they would be pretty common by now ? I'd be tempted to use one of
those radar/doppler door opener modules (the kind that works with rf) and
just use a pic as a frequency counter on the output signal. Some
calculations are in order but the error of the oscillator should keep
total doppler error well below 1% and counter error at quartz accuracy.
For a quick test just wire headphones to the unit held outside the window
pointing down and backwards to hear the tone (probably not by the person
who is driving).

Peter

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