Matthew Smith wrote:
Quoth Poul-Henning Kamp at 2010-02-23 20:22...
In message <4b83a33c.1010...@smiffytech.com>, Matthew Smith writes:
Simple and rather fundamental question: does the common or garden
rubidium oscillator constitute an atomic clock?
Yes.
...
Many thanks for the responses and ensuing discussion that has
considerably value-added to the yes/no nature of my original question ;-)
Now I know a lot more about primary/secondary standards than I did a
(9,192,631,770 Cs wobbles * 86400) ago.
I can now proceed with my unconventional calendar design (a cascade of
dekatrons) knowing that it will be driven by an atomic ticker.
BTW: does anyone know if a 0.55V p-t-p sine wave from an Rb source would
be enough to clock an Atmel AVR microcontroller? The crystal/clock
input *is* an amplifier, but didn't know if I'd need to do anything to
the signal first, to get it closer to the 5V logic level.
Cheers
M
Matthew,
The signal you describe could be fed through a small-value capacitor (perhaps
100 pF) right into the microcontroller. The amplifier must be internally biased,
otherwise it wouldn't work with a crystal.
You will want to put a protection circuit on the input if you have an exposed
coax connector leading to the outside world, in case of a static discharge to
the center pin of the cable. A series resistor of several Kohm followed by the
capacitor in series with the signal, plus a pair of 1N4148 diodes connected in
reverse-bias to Gnd and Vcc from the input pin of the MCU, are usually sufficient.
--David Forbes
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