Ben: Be careful.
Most GPS receivers send out the serial message after the tick, that tells you what the time of the tick was. Read the manual. If you want to drive a clock display with a GPS, you pretty much have to have an independent time system that advances on the tick, then validate it when the serial message shows up. --- Graham / KE9H == On Tue, Jun 6, 2017 at 6:46 PM, Ben Hall <kd5...@gmail.com> wrote: > Good evening all, > > There is a saying: "a man with one watch knows the time, a man with two is > never sure." Clearly, this man wasn't a timenut and didn't have GPS. ;) > > I've been working on the Arduino code for the TruePosition boards that > quite a few of us have bought from the e-place. > > It's my first real foray into both Arduino and the C language. (About a > million years ago I was reasonably competent with FORTRAN...the 1977 > version...) It's mostly working - I can receive and display pretty much > everything that comes out of the unit minus a few parameters. I can > display it all on three pages on a 4 line by 20 character I2C display. > Currently, the pages are selected by grounding out one of two pins, or > having nothing grounded. Eventually, I'm going to change this so that it > changes display pages when a button is pressed. I don't have lat/long > display yet, nor can I handle doing a survey, but those are coming. > > My code probably would make a real programmer vomit, but hey, it works. :) > > Back to the man with multiple watches. I was having a very frustrating > issue with my TruePosition and Arduino code being one second behind my > other sources of time. I went round and round, trying to figure out why > the TruePosition thru the Arduino was a second slow. In the end, it turns > out that it wasn't slow...it was correct...but that my other sources of > time have errors. > > I finally proved this to myself by firing up an old Trimble Lassen LP GPS > board unit equipped with a 1PPS tick light and serial output...and it was > clear that it matched the TruePosition after correcting for the fact that > my TruePosition / Arduino code only updates the display when 1PPS is > asserted high...but that the Lassen LP displays the serial message before > it becomes valid at the next 1PPS tick. > > I was slightly embarrassed...I should have known that the other sources of > time all had sources of error beyond my control. I should have trusted the > TruePosition as being the purest, least complicated, and the path I knew > the most about between GPS and my eyeballs. > > So for a while...the statement was true. With my multiple sources of > time...I really didn't know the time. But it was also untrue, as when I > got agreement between two very "pure" sources of time, I knew everything > else was wrong. ;) > > I'm getting to the point that once I've got the button logic working, I'll > send out my source to anyone who wants to take a look at it or use it. I > will stipulate one condition - you can't make too much fun of how poorly > programmed it is. ;) > > thanks much and 73, > ben, kd5byb > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.