Thanks for all the help.  After struggling with the circuit for several
hours I tried swapping out the ceramic resonator got a new ceramic resonator
and tried it.  Magically, it worked...

I am not sure quite sure why that worked, but it could be as simple as the
fact that that resonator was bad or the solder joints were fouled up.  With
something so cheap I should really keep extras on hand to swap during
trouble shooting.

Anyway, thanks again for the suggestions.  I am just in high school and
trying to learn electronics.  Often just reading through this weblist has
been more educational than any of my classes and your responses have been
really informative.

For example, I haven't come across this "powered clock" before.  Digikey and
Google dont seem to show anything with my search terms.  Anyone have  a part
number or link to a datasheet?  I originally chose a ceramic resonator for
my design because I read they were more robust than crystals and I wanted
this to go inside a model rocket. Since the ceramic resonator  is  working,
I will keep it for this version, but maybe for another revision or other
project this powered clock would be better.

Regards,
Adam



On 12/10/06, James Nick Sears < jnsears@jamesnsears.com> wrote:
>
> For a dollar or two, you can be free of all of these issues with a
> little powered clock.  Four pins, Vdd, GND, CLKOUT, and something
> else (probably an enable-like function) and you are good to go.
> 40MHz, no problem.  Just set your clock config flag to EC (external
> clock).  Available in through-hole or SMT (actually the surface mount
> version is smaller or at least similar to the SMT crystals I used to
> use).
>
> I've spent way too much time already in my young life fighting with
> crystal oscillator circuits.  Anything of mine in the future that
> isn't intended for mass mass production (and maybe stuff that does)
> will have a powered clock, unless there is some reason not to that
> I'm not aware of.
>
> -n.
>
>
> On Dec 10, 2006, at 8:11 PM, Bob Axtell wrote:
>
> > Adam stambler wrote:
> >> Hi, I was wondering if anyone could provide some oscillator
> >> guidance.  I am
> >> trying to run a 16f690 off a 20 mgherz ceramic resonator with
> >> built in
> >> capacitors.
> >>
> >> I think i have all my my programming correct, but when I go to
> >> turn it on,
> >> it does not work.  The oscillator does not start up.  However, if
> >> I try to
> >> measure the voltage with my multimeter and touch the Clock input
> >> pin, the
> >> PIC starts to work.  There is about 2.3V on the clock output and
> >> input pin
> >> .
> >>
> >> Right now i have a 1 mega Ohm resistor across the input and output
> >> leads of
> >> the resonator like the datasheet said for it to have. I am running
> >> the
> >> resonator in HS mode.
> >>
> >> My guess is that my programming is correct but there is not enough
> >> drive to
> >> get the oscillator going.  Unfortunately, I have no idea about how
> >> to fix
> >> the problem.  This is my first oscillator circuit which I am using
> >> for a
> >> school project.
> >>
> >> Anyone have any ideas?
> >>
> >> Thanks,
> >> Adam Stambler
> >>
> > I have never been able to get reliable startups with the 20M seramic
> > resonators. The fastest reliable speed
> > for me was 16M. And I love these critters dearly.
> >
> > I believe the phase-shifting caps do not quite match the Microchip
> > oscillator. Drop back to a lower speed
> > or tinker with cap values. Incidentally, the ones by Murata may run
> > at a
> > slightly faster rate.
> >
> > --Bob
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>
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