I imagine it is similar to the method of measuring the thickness of very thin sheets or coatings. You can do it using interference colors (like the colors you see on an oil slick). Don't even need any measurement equipment except your eyeball since the reflected color varies with the thickness. Color blind people not allowed.
What makes you think a processor has to do the measurements in software? That would truly be dumb. Time measurements in the 1ns range aren't difficult at all, though I agree this isn't what they're doing. Measuring even to 1ns is 1 foot accuracy; hardly useful.
No, what would truly be dumb is to reply when you don't know what you're talking about. The measurement IS being done in software. Where else is it going to be done? Do you think the light wave computes the distance itself and passes the data to the microcontroller to display it?
The microcontroller has an on-board timer and uses it to measure the phase difference, in time (T). But instead of measuring the time for the lightwave to bounce back, the phase shift is measured (in TIME). The transmitted frequency (R) is known so it then computes D, where D = R x T.
Mike
Nice, but ignorant comment.
That would truly be dumb. Hardware can easily measure a nanosecond. Software can format the output of the hardware so a human can read it, but a software timing loop differentiating 1ns events? You're on drugs.
You really are ignorant. Have you ever considered a simple counter running at a GHz, or maybe interferometry to measure the phase relationship of the sent and received signal. The microcontroller certainly *not* going to be able to discern a 1ns signal, even it it does operate at a couple of GHz.
The timer would have to operate at a GHz, along with the I/O in question, just to get one *foot* resolution. Hardware can be used to measure the phase relationship without having to operate at
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