[time-nuts] Using a frequency synthesizer replacement for motherboard oscillator

John Ackermann N8UR jra at febo.com
Sat Dec 1 00:42:28 UTC 2012


In this case, you're not looking for the RTC but rather the clock that drives the COU, which is what drives the system clock.  On most systems, the RTC is read only at startup and is not used once the system is running.

John

On Nov 30, 2012, at 6:30 PM, Eric Garner <garnere at gmail.com> wrote:

> the actual RTC on modern (Intel based) PC's is driven from a standard
> 32,768 Hz crystal attached to the PCH. some of them are in incredibly small
> packages now instead of the old tuning fork-in-a-can ones. peeling off the
> load caps and crystal from the board would allow you plenty of spaces to
> tack down a lead from an external synthesizer.
> 
> 
> -Eric
> 
> On Fri, Nov 30, 2012 at 3:04 PM, bownes <bownes at gmail.com> wrote:
> 
>> It all depends on what clock your talking about. Any given PC probably has
>> more than one oscillator onboard.
>> Generally there will be one for the CPU, one for the display circuitry,
>> and probably one for the real time clock.
>> 
>> Presuming you are talking about the CPU clock, it should be fairly
>> straightforward to find the oscillator package on the motherboard find the
>> pin with clock output and feed your clock input there.
>> 
>> On Nov 30, 2012, at 16:59, Bob Camp <lists at rtty.us> wrote:
>> 
>>> Hi
>>> 
>>> It's most commonly done with things like a Soekris 45xx series board.
>> You don't need anything very exotic for the frequency conversion. The
>> jitter in the PC is way worse than what the external chips will be creating.
>>> 
>>> The real question is - what is the "magic frequency" on the particular
>> mother board you are going to modify? Once upon a time they all were a
>> pretty predictable 14.xxx MHz. These days, who knows what's going in where…
>>> 
>>> Bob
>>> 
>>> On Nov 30, 2012, at 4:55 PM, Sarah White <kuzetsa at gmail.com> wrote:
>>> 
>>>> Has anyone ever used a TAPR clock block or other frequency synthesizer
>>>> to sort the clock drift / timing problems on a regular computer? I'll
>>>> probably end up with a used dell or IBM workstation for this purpose.
>>>> 
>>>> Recently, I came across a low-cost frequency synthesizer capable of
>>>> using a 10mhz frequency reference (planning on using the thunderbolt
>>>> GPSDO I'm working with once I manage to sort out the temperature issues)
>>>> 
>>>> http://www.tapr.org/~n8ur/Clock-Block_Manual.pdf
>>>> 
>>>> ^ TAPR "Clock Block" has an installation example for how to do what I'm
>>>> planning with a Soekris net4501 low-cost / low-power embedded device...
>>>> 
>>>> What I'm hoping to figure out is how to do the same, except on a proper
>>>> computer such as the local used ones I'm able to get for less than $200
>>>> with 2ghz with 30GB hard disk, 512mb or more ram, etc. So I figure this
>>>> should be fine for what I'm planning.
>>>> 
>>>> Example of what I'm trying to do, though based on the low-power embedded
>>>> Soekris net4501 system from the TAPR manual's example section:
>>>> 
>>>> http://www.febo.com/time-freq/ntp/soekris/index.html
>>>> 
>>>> ^Aren't those the photos from clock block frequency synthesizer manual?
>>>> 
>>>> Again, I'm wondering if anyone has opinions or experience about doing
>>>> such things with NOT an embedded system (as I said, can get a nice 2ghz
>>>> or so machine for less than $200 locally at a brick and mortar shop
>>>> within walking distance)
>>>> 
>>>> Thanks in advance,
>>>> Sarah
>>>> 
>>>> 
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
>>>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>> and follow the instructions there.
>>> 
>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
> 
> 
> 
> -- 
> --Eric
> _________________________________________
> Eric Garner
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



More information about the time-nuts mailing list