Chris, The beginning of the second, and the starting of the 10ms samples is detected with a tight asm loop. (Soon to be replaced with a high priority interrupt line) Once detected the sample portion of the state machine runs at 10ms. And terminates at the 990ms (99th sample), I process the received bit and go back to the wait_for_start state.
My thoughts are that the second starts are where the accuracy needs to be. I'm starting to get an idea of its pps accuracy (or do I really mean "stability" ?). I ran a quick test having the mcu measure what it thinks the length of a second is using the internal timers (auto reloading). I need to do more research on how to properly characterize it. -lenny On 3/27/11, Chris Albertson <albertson.ch...@gmail.com> wrote: > On Sat, Mar 26, 2011 at 4:31 PM, Lenny Story <le...@codematic.com> wrote: >> Chris, >> My design isn't really that sophisticated hardware wise. Its an 8051 >> variant, and the CMMR-60P which can be obtained from Sparkfun.com. I do >> wind my own antenna, which is just a quad, made from PVC and a metal >> electrical box. The circuit sits in the center. It's done with a 2.5 >> inch >> square, 4 layer board from pcbexpress.com. >> The software samples the bit signal coming from the CMMR, every 10 ms >> (essentially), and uses a 100 bit array to qualify it using a weighting >> algorithm. The start of the bit train, and with it the sequence of 10ms >> samples, is essentially polled very fast to catch the beginning of the >> second as soon as possible. > > So you are looking at the output bit of the CMMR-60 once every 10 ms? > Then I'm guessing you will not get uS level precision. > The software I'm writing runs under Linux and reads the bit every 1 > msBut I was wondering if I should do better and try for uS level > timing > > I think your success with receivig WWVB must be the antenna. Could > you say more about it. > ===== > Chris Albertson > Redondo Beach, California > -- Sent from my mobile device _______________________________________________ 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.