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



chris <chris-nospam@xxxxxxxxxx> wrote:
> On 06/16/22 16:20, Jim Pennino wrote:
>> 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".
>>
>>
> 
> You need a ttl to rs232 converter.

That is what a level converter 3.3 to 5 is.

The RS-232 standard mark is +3 to +15 V and space is -15 to -3 V, which
means a 0/3v level converter to -5/+5V meets the RS-232 standard.
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