[time-nuts] Scope Clock

Eric Fort eric.fort at gmail.com
Thu Aug 2 17:42:25 UTC 2007


jan seems to be having a bit of trouble posting so I'll add his off list
reply to the list discussion.  I too have one of these on it's way and look
forward to  building it.

Eric

Hi, Eric.



I saw the discussions on the TimeNuts list but haven't figured out how to
respond to the list so I'm emailing you directly.



The DAC used on the clock has indeed a fairly high output impedance which
makes the outputs sensitive to noise. This is minimized by a careful layout
and a ground plane around the traces. The other result is that there are
visible vector retrace lines (when the beam jumps from one location to
another) if there is a significant capacitance on the outputs. This effect
is minimal when using 10X probes.

There is a suggested hardware modification using 2 load resistors in the FAQ
that will significantly reduce the output impedance (thus the capacitance
sensitivity) and also will reduce the voltage swing, which will reduce
non-linearities. Take a look at:
http://www.dutchtronix.com/ScopeClock2-6faq.htm#LoadResistors



Your clock kit is on the way



-Jan-



On 8/2/07, Robert Atkinson <robert.atkinson at genetix.com> wrote:
>
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+eric.fort=gmail.com at febo.com RETRY
>
> Hi Nigel & Eric,
> I've just order one of Jan's clocks. He has just got PCB's back in
> stock.  I looked quite carefully and 1PPS is standard. The board has a
> PCF8563 RTC chip with a 1PPS output that is used by the microprocessor.
> The signal line has a 2 pin header that has a jumper for internal 1PPS
> or you can use the header to supply an external 1PPS.
> The clock has two basic modes of operation, one where the microprocessor
> just reads the RTC and displays that time, the other (AVR Master Clock)
> where it counts the 1PPS. While in master mode it updates the RTC to use
> for reversion in case of power fail (The RTC has battery back-up on the
> board).
> It looks like a great little board. The only limitation I can see is
> that the ADC's are un-buffered R/2R ladder types with fairly high output
> impedance. I want to drive a small X-Y display so I think I will have to
> build a buffer amplifier.
> I'll keep the group up dated.
>
> Robert G8RPI.
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of GandalfG8 at aol.com
> Sent: 31 July 2007 23:32
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Scope Clock
>
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+robert.atkinson=genetix.com at febo.com RETRY
>
>
> In a message dated 31/07/2007 23:23:38 GMT Daylight Time,
> eric.fort at gmail.com writes:
>
> as  ordered will these boards accept 1pps or was yours a  special?
>
> Eric
> kg6kqt
>
>
> -----------
> Hi Eric
>
> Take a look at.....
>
> _http://www.dutchtronix.com/ScopeClock.htm_
> (http://www.dutchtronix.com/ScopeClock.htm)
>
> It looks like the 1PPS is standard.
>
> I've got a 12 inch X-Y display doing nothing right  now......
> and I'm very tempted to have a play with one of these:-)
>
> regards
>
> Nigel
> GM8PZR
>
>
>
>
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