[time-nuts] Designing an embedded precision GPS time

Leo Bodnar leo at leobodnar.com
Wed Nov 1 00:06:06 EDT 2017

> From: Attila Kinali <attila at kinali.ch>
> Basically, all you have to do is use an SBC that runs linux and has
> a GPIO with an interrupt to act as a PPS input. Attach a GPS receiver
> and you are almost done. The cheapest option are probably the i.MX233
> based ones (go as low as €20). 

Thank you, Attila, this sounds like the way to go - perhaps I can repackage this solution in a smart attractive enclosure and market it as a high performance product.  
I was a bit behind the curve on recent developments - do you have a suggestion for the best linux running SBC and cheap GPS suitable for this?

>> I am not measuring any frequencies - the whole device runs synchronously hard-
>> locked to GPS time when it is available and freewheeling when not.
> You should have a control loop somewhere, which explicitly or implicitly estimates the frequency of the TCXO. 
> The time-nuts archives are full with discussions how to do such
> control loops and improve hold over performance. Though there
> weren't many in the last 2-3 years. John Vigs tutorial is also
> a good start.

OK, so I need to introduce additional TCXO and a control loop to improve the holdover performance?


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