On 24 Feb 2016, at 4:30 pm, Chris Albertson <[email protected]> wrote:
> A simple GPSDO is, well, simple. All you do is compare the phase of > the PPS to the phase of the 10MHz crystal and then adjust the > frequency of the crystal to keep the phase difference constant. Can > be done all in software by a $2 micro controller chip. By Time Nut > standards the performance will not be top notch but compared to your > NTP server it could literally be 10,000 times better A while back I > tried to build the cheapest and simplest GPSDO possible and except for > the price of the crystal and GPS receiver I spent about $5. > Performan ce was such that when I put the cheap GPSDO 10MHz output > and my Thunderbolt both on a dual trace scope I could see some > movement in phase over hours long time but over days in stays locked > > First divide the 10MHz crystal to say about 1Mhz using a TTL divider. > Some (most) micro processor chips have a way that an external signal > can trap the current value of a counter. Let both the PPS and the > 1Mhz do this and look at the difference in counts. Adjust the crystal > so the difference remains constant. Don't worry about details, that > is for latter make it as simple as possible. Improvement is for > version #2. This appeals to me, but I think it’s currently beyond my level of knowledge. However, I’ve decided to build this: http://www.hackersbench.com/Projects/1Hz/ which has an easy to follow diagram. Parts have cost less than £5. I’m not expecting great things from it by any means, but it’s something I can get my head around and should improve my understanding (a little). _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
