[time-nuts] PICTIC II

Steve Rooke sar10538 at gmail.com
Sat Jun 26 10:38:29 UTC 2010

Ah! Sounds like you were subjected to the "Bruce factor". It's a case
of publish a design and then expect to be insulted about it. I'm glad
you weathered the storm and wish to thank you for your present.


On 26 June 2010 19:11, 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.
> http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:pictic
> 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.
> Richard
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Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein

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