[time-nuts] Bye-Bye Crystals

Scott Stobbe scott.j.stobbe at gmail.com
Tue Mar 14 13:16:24 EDT 2017


Not only that. Good luck finding a datasheet with *any* analog
specifications for its internal oscillator. Here are the pins for an
external crystal. The microchip PICs are nice, they give you the goldilocks
selection for drive level a little cool, a little hot, maybe just right.

On Tue, Mar 14, 2017 at 8:04 AM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> > On Mar 14, 2017, at 4:44 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> >
> >
> > artgodwin at gmail.com said:
> >> I'm not after quality - I do have an application in mind but it doesn't
> need
> >> to compete with mass production. Just wondering if it's feasible to make
> >> something crude that will resonate.
> >
> > Are you doing this for fun or ???
> >
> > Feasible?  Sure.  Cheaper?  That depends.
> >
> > The cost difference between a complete oscillator package and a simple
> > crystal is tiny.  The osc is often cheaper if you include board space or
> > engineering time.
>
> Purchased in volume, the difference it the price of a crystal vs a
> complete XO
> is enormous. You will see at least a 10:1 cost savings on the crystal and
> likely
> more than that.  Simply attaching a crystal to the internal oscillator
> inside a
> chip is nearly zero engineering cost.  If your product is cost sensitive
> and
> not super tight tolerance … you go with the crystal.
>
> Bob
>
> >
> > Is your background digital or analog?  Do you want a sine wave or a
> clock?
> >
> > My background is primarily digital.  If the chip you are using has 2 pins
> > setup to drive a crystal, you can probably get it to run reliably by
> > following the data sheet and/or app notes.  The usual recipe is 2 tiny
> caps
> > and a big resistor.  (big in resistance, not physically big)
> >
> > An advantage of using a crystal with the on-chip amplifier that I didn't
> > mention last time is that you save the osc power if you power down that
> > corner of the chip.
> >
> > If you want a sine wave, you are out of my comfort zone.  I'd probably
> look
> > in ham radio literature.
> >
> > They make logic chips like a 74HCU04, U for unbuffered.  One of their
> uses is
> > for making oscillators.  I've never done it.  Try google.
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
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