[time-nuts] Rb Oscillator - rather fundamental question

[David Forbes]

Matthew Smith wrote:
> Quoth Poul-Henning Kamp at 2010-02-23 20:22...
>> In message <4B83A33C.1010903 at 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