[time-nuts] Scope Clock
GandalfG8 at aol.com
GandalfG8 at aol.com
Thu Aug 2 05:53:49 EDT 2007
In a message dated 02/08/2007 08:48:14 GMT Daylight Time,
robert.atkinson at genetix.com writes:
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
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.
I ordered a couple the other night too:-)
I meant to report back at the time but it was very late when I finished.
I'm also planning on using an X-Y display, but had just assumed the inputs
would be high impedance and hadn't thought about buffering. Good point though
and something I will need to check.
One other limitation is the resolution, again something I hadn't considered
before ordering, so a smaller X-Y display might be a much better option than
the 12 inch unit I had planned on using.
These were the comments I received from Jan....
You can use the clock on an X-Y display, though 12” is pretty big
(resolution of the clock is 254 by 254 pixels).
Most X-Y displays like a signal in the 0-1V range and the hardware mod
described in the FAQ
(http://www.dutchtronix.com/ScopeClock2-6faq.htm#LoadResistors) will cause the clock to generate exactly that voltage range (when using 1X
probes or straight cables)
It certainly does look like a great little board, and good value too, I
think it'll be a fun project.
Perhapst the biggest problem might be that of "little" projects growing into
I'm already thinking about centrally mounting an X-Y display at the top of
one of the racks, if I can spare the space, with clock module built in, and
perhaps even its own GPS module for the 1PPS:-)
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