/2/2022 3:27 AM, time-nuts-requ...@lists.febo.com wrote:
Subject:
[time-nuts] Re: 32.768Khz Crystal Trimming
From:
"Richard (Rick) Karlquist"
Date:
4/1/2022, 12:34 PM
No one mentioned tempco, so I will. Ideally you should do your
calibration at a temperature corresponding to the
Hi
The cap ratio very much depends on how the internals of the chip
got done. Since you have zero info on that, it’s best to stick with the
ratios and approximate values shown in the app notes.
The most common way to get a fine grain tune is to put something
large in series with the crystal (ma
After playing with cap values the crystal is running about 6.5ppm fast.
Plenty good for what it is. Of course this was with a sample size of 1.
Being a time-nut, I did try a few different cap values just to see if it
could be made any better. The Next closest cap combo gives 8.3ppm slow.
Putt
to all who replied. This should be enough to keep me busy over
the weekend!
Dan
On 4/1/2022 12:26 PM, time-nuts-requ...@lists.febo.com wrote:
Subject:
[time-nuts] Re: 32.768Khz Crystal Trimming
From:
"Bernd Neubig"
If you do not want to make it a time-nuts style research project,
Hi
The typical 32 KHz crystal has a parabolic tempco. It peaks at kinda
sorta room temperature. This makes it work pretty well on a normal
wrist.
As you get away from ~ 25C, the frequency drops. Since it’s a
parabola, the further away from room you get the faster it drops.
Something in the 1
No one mentioned tempco, so I will. Ideally you should do your
calibration at a temperature corresponding to the long term
average in your workshop. If the crystal is in a piece of
equipment with a temperate rise, it should be accounted for,
and then going forward you have to leave the equipment
Hi,
If you do not want to make it a time-nuts style research project, but just
look for a quick fix - here is a rule of thumb:
This kind of crystal usually has a trimming sensitivity of around -10
ppm/pF. This means, if you increase the value of both capacitors on either
side by 2 pF will increase
Remember that the load cap value in the data sheet isn't what you fit in
the circuit.
First deduct the total stray capacitance on the pcb and the IC
connections, then double the remainder... that's the value you place
either side of the crystal.
E.g. if the data sheet says 12.5pF and you estim
version of the 32.768
kHz oscillator or measuring the RTC against a known time source.
-John
-Original Message-
From: Bob kb8tq
Sent: Friday, April 1, 2022 8:01 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Re: 32.768Khz Crystal Trimming
EXTERNA
Hi
Given the (very normal) lack of information on the crystal,
it becomes a “try it and see” sort of thing. They seem to
want 12.5 pf as the load cap for the first one listed on the
data sheet. How far off of that is your circuit as it sits?
First step would be to take the “output” cap up one v
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