On Wed, 19 May 2004, Robert B. wrote:
> Does anybody know of a way to make a PIC measure time intervals shorter
> than it's instruction cycle?  I need to measure the time between a
> transmitted and a reflected radio pulse in the 3 ns range, and would
> like to do it with a PIC.

You might consider producing a well defined (voltage and current) pulse
of the length you wish to measure, use that to squirt a bit of charge
onto a capacitor, and then measure the voltage off the capacitor later.
By choosing appropriate signal levels and RC values you can adjust this
idea for the range of pulse lengths that you are interested in.

Long ago someone experimented with the idea of driving pulses into a
"flash" AtoD converter.  Some of these have a uniform RC ladder network
inside and that posed some interesting possibilities.  But I don't know
whether that was later patented or not, I was gone before that was done.
Check carefully if that matters. There were several enhancements made in
the implementation of this idea.

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