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From: "John Jardine"
Subject: Re: 100Hz from 25.6kHz crystal.
Date: Tue, 3 Dec 2002 14:46:52 -0000
NNTP-Posting-Date: 3 Dec 2002 14:34:46 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Peter Nolan wrote in message
> I just got some 25.6kHz crystals from www.digikey.com I want to get
> from the O7 output of a 4060 14 stage ripple-carry counter/divider and
> oscillator. I am trying to use the Pierce oscillator( I wish I knew more
> about the Pierce oscillator than I do which is close to zip) that is drawn
> in the Philips datasheet at:
> From here one can download the datasheet. It downloads in seconds.
> In spite of my best efforts I cannot coax the oscillator to oscillate at
> 25.6kHz. Instead it oscillates at around 422kHz. I have tried varying
> and C3 over the recommended ranges but to no avail.
> The datasheet for the crystal(C-2 type) is at:
That is one weird crystal frequency!. Crystals that work at such low
frequencies are not much good at keeping time and are also *very* sensitive
to oscillator drive levels.
Your oscillator is preferentially oscillating without the crystal actually
forming part of the circuit.
The feedback resistor (pins 10-11) needs to be about 10Mohm and the series
power limiting resistor needs to be about 330kohms.
Much better would be to use a standard 1.6384Mhz Xtal using your normal PDF
circuit values (uses all the dividers in the 4060). This will give a solid
100Hz with *much* better stability.
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