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[questions] Re: GPS+PPS vs NTP server, why a huge offset ?



Thibaut HUMBERT <planetibo@xxxxxxxxx> wrote:
> Le jeudi 16 juin 2022 à 16:37:33 UTC+2, David Taylor a écrit :
>> On 16/06/2022 10:00, Thiebaud HUMBERT wrote: 
>> > To do the inversion, I just changed the "Pulse Mode" parameter to "Falling edge" from "Rising edge". 
>> > The offset induced by the "pulse length" has disappeared. 
>> > But there is still an offset of around 10.3ms, which I think is induced by USB as explained in this article about other chipsets (https://lists.freebsd.org/pipermail/freebsd-usb/2019- August/016078.html)
>> Yes, Thiebaud, USB is not good enough for PPS signals! 
>> 
>> See if your motherboard has a true serial port - perhaps just as a header but 
>> not a back connector. If not, just set the offset of the PPS to ~10.3 
>> milliseconds (10.3 - IIRC the offsets are in milliseconds but please check). 
>> Plus or minus 10.3, try it and see! Not perfect, but better than nothing. 
>> 
>> You might find better results using that GPS/PPS with a Raspberry Pi as a 
>> stratum-1 server and offering that as a server on your LAN. 
>> 
>> Cheers, 
>> David 
>> -- 
>> Cheers, 
>> David 
>> Web: http://www.satsignal.eu
> 
> 
> I have a serial port, but I don't know how to convert the PPS output (0 / 3.3V) to RS232 (-5V / +5V).

You go to amazon.com and search for "level converter 3.3 to 5".
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