I would run a test and track turn ON/OFF times against varying intensities to get enough data to chart/graph. THEN, you can make informed decisions about intensity level, whether you want to consider turn off time, etc.
This could become quite voluminous... data acquisition-wise and just the sheer amount of information. ______________________ Clay Autery, KY5G MONTAC Enterprises (318) 518-1389 On 7/16/2016 2:08 AM, John Swenson wrote: > Yes, I was planning on using a high speed photo diode to actually > measure the turn on time of the digits. I hadn't thought of the turn > OFF time, do I want the old digit to be turned off before the new one > lights up or for them to be overlapping? I have been thinking about > what threshold to use, 50% intensity is probably about as good as any > other. It might turn out that different digits turn on differently, so > I will have to calibrate each one separately. > > John S. > > > > On 7/15/2016 4:57 PM, Chris Albertson wrote: >> If you are going for the sawtooth correction then you also might want >> to add some kind of forward correction for the delay in the tubes and >> the drivers. Your MOSFET gates the nixie tube itself have capacitance >> and switch times that will delay the switch of the display and of >> course the digital processing in the FPGA takes some number of >> nanoseconds. I think you might need some way to actually measure all >> of these as any estimate might be your single largest source of error. >> I don't know how to measure it. Perhaps a pair of phototransistors >> one aimed at a PPS LED and one at the nixie tube. This unknown delay >> is likely larger than the sawtooth correction. at this level you >> might have to define when a digital is actually "on" as there is >> likely some thermal constant and the numbers don't light up instantly. >> I'd bet the turn on time is larger than the sawtooth correction. >> What is "on"? 50% brightness? >> >> It gets hard when you start caring about tiny increments of time. I >> have a mechanical clock, about 14 inches in diameter that is slaved to >> NTP. The designer took a big short cut. Time is kept internally at >> the hundreds of microseconds level and the pulse goes off to the >> stepper motor at the correct time well at least at the 100+ >> microsecond level but the hands don't move instantly because (1) >> slight gear backlash and (2) they have mass. I can actually SEE the >> delay with my eyes. The designer must have forgotten that a "move" >> command requires some milliseconds to execute (I'm thinking about >> 100ms or more). I don't care but it's fun to think the actual display >> is 10,000 times less accurate then the internal timekeeping. You >> don't want this to happen to happen nixie clock >> >> BTW I did not build my mechanical NTP clock. I got a free broken >> clock and had to fix it, cut and soldered a few traces, fixed some >> cracked parts and learned how it works in the process. >> >> Finding which PPS to use is easy, you can do that by eye. Compare the >> serial data stream to the time on your NTP sync'd computer. A full >> second off problem is easy to see. >> >> >> On Fri, Jul 15, 2016 at 3:53 PM, John Swenson >> <johnswens...@comcast.net> wrote: >>> Yep, that is theory. The fun part is going to be getting the right >>> edge for >>> the new PPS. Half the time it will the one before the PPS from the >>> GPS and >>> half the time it will be the one after. From the sawtooth data I >>> should be >>> able to figure out which is which to align it to the new LO. >>> >>> John S. >>> >>> >>> On 7/15/2016 3:17 PM, Bob Camp wrote: >>>> >>>> Hi >>>> >>>> If you are going to go “full boat” then you probably should get the >>>> sawtooth correction out of >>>> the GPS and feed that into your control loop. You will need >>>> something you >>>> can run out at the >>>> “few hundred seconds” sort of time constant. >>>> >>>> Bob >>> >>> >>> _______________________________________________ >>> 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. >> >> >> > > _______________________________________________ > 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. _______________________________________________ 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.