[time-nuts] PICTIC II
jgray at zianet.com
Mon Jun 28 00:59:29 UTC 2010
I'm just a hobbyist and have a lesser understanding of this stuff than
yourself. I'm interested to hear more about your project and also the
PICTIC+ II that is mentioned on the web page. Some specs would be nice
and if you have any type of user manual, that would even be better. If
a kit is in the works, I'd be interested.
Has anyone run a side-by-side comparison with an HP 5370 or similar
TIC? Obviously, the resolution would not be the same, but it would be
interesting to see how they track.
Thanks for expending the effort to bring us a low cost TIC.
On Sat, Jun 26, 2010 at 1:11 AM, Richard H McCorkle
<mccorkle at ptialaska.net> wrote:
> Fellow Time-Nuts,
> When I first uploaded the Simple PICTIC interpolating time interval
> counter to the K04BB site in 12/08 and presented it to the group as
> a Christmas present my goal was to get amateurs building their own
> interpolating time interval counters for GPS monitoring and making
> improvements to my design. The interpolator in the PICTIC was
> “borrowed” from an early HP counter with minor modifications so I
> didn’t design it and had no personal attachment to it. My forte is
> writing PIC assembly code for time and frequency applications and
> I make no claims of being a hardware design engineer. I am just
> an amateur interested in writing PIC code and was building my own
> PICTIC. I wanted to share my design, as I couldn’t afford multiple
> commercial high-resolution time interval counters to monitor my
> standards and thought there might be others with similar needs that
> could benefit from a low cost TIC design.
> Testing the HP interpolator with my code showed it had sufficient
> capability to be useful in a low cost TIC for GPS monitoring where
> a modest resolution increase was desired. In response to my posting
> I was subjected to a barrage on the shortcomings of the interpolator
> with few comments on the rest of the design. I responded to the
> comments based on test results showing it was sufficient for purpose
> and suggested trying the design before saying it wasn’t usable. The
> response returned was “I wouldn't waste my time with a circuit that
> is inherently as non-linear as yours.” so the rest of the design was
> discounted by others as not being worth the time to evaluate. I began
> a discussion on line about the interpolator, which was destined to
> turn into a long and annoying thread similar to the recent TPLL
> discussion. Rather than getting into it on line I elected to put a
> stop to it by saying publicly I was at fault and would begin further
> study, as I am not as thick skinned as Warren. Subsequent independent
> testing of the PICTIC by William Riley showed the interpolators were
> linear to the 10-bit ADC resolution over the measurement range with
> suitable accuracy for the intended application of GPS monitoring
> as originally stated.
> Over the last 18 months I have developed a new diode switched
> interpolator based on the comments made on line and have thoroughly
> tested it. Some suggestions made improvements in the performance and
> some resulted in poorer performance. I incorporated those suggestions
> that made improvements, eliminated those that made things worse, and
> once I was satisfied I sent the revised interpolator design directly
> to Bruce off line. Based on comments and suggestions he returned
> during a long series of emails I incorporated additional changes in
> the code, front-end, and interpolator designs and tested those
> changes until I was satisfied with the performance and he had no
> further comments. I am finally satisfied with the new design and
> admit that by incorporating the majority of the suggestions made
> the new interpolator has significantly better linearity than the
> HP interpolator used in the PICTIC and it is now suitable for
> higher resolutions.
> I was reluctant to post the PICTIC II in this forum, as I don’t
> want to get in another public discussion of its faults without any
> discussion of the merits of a $50 serial output interpolating TIC
> on a 3.8” x 2.5” thru-hole board designed for amateur construction.
> The K04BB WIKI PICTIC page was recently updated to include the
> PICTIC II code and ExpressPCB board layout and schematic files for
> those that might be interested.
> The PICTIC II incorporates the new interpolator, requires a delay
> between the inputs, and uses a low stability XO timebase with
> software peak detection for calibration with provision for an
> external timebase like the PICTIC to minimize size and cost.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts