Subject:
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Re: RCX has a fast clock, was Re: Rolling ball clock revisited
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Newsgroups:
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lugnet.technic, lugnet.robotics
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Date:
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Wed, 8 Dec 2004 14:08:54 GMT
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Viewed:
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3138 times
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> I suppose that this problem comes from bad capacitor loading of the crystal used
> on RCX. Crystals need to see some capacitance to oscillate at the right
> frequency, generally in the 10 to 30pF range. Even if PCB traces themselves
> bring some capacitance, there is no added caps on RCX PCBs (see
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38746), this should be enough to
> explain the problem.
As David Ward suggested me, the oscillator is most probably equipped with a
ceramic resonator with built-in capacitors. This explains the low precision of
the clock (tolerance for ceramic resonators is in the 1% range while for
crystals it is in the 0.01% range). Resonators are cheaper too ;o)
Philo
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