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Why is the 32 kHz crystal oscillator used in RTC, instead of the 16 kHz?
- Thread starter Lentol
- Start date
A 32 kHz "crystal" actually is a type of tuning fork. This is used because at these low frequencies it is much smaller than a standard AT cut crystal would be. Still, size is everything inside a wrist watch. 32 kHz was a tradeoff between size (higher freq = smaller) and circuit complexity (higher freq = more divider stages).
It has nothing to do with accuracy. A 1% error in a 10 MHz oscillator, a 10 kHz oscillator, and a 10 Hz oscillator will produce the exact same 1% error percentage when they are divided down to 1 Hz.
ak
It has nothing to do with accuracy. A 1% error in a 10 MHz oscillator, a 10 kHz oscillator, and a 10 Hz oscillator will produce the exact same 1% error percentage when they are divided down to 1 Hz.
ak
He was not asking, he was telling you - he already had the link and the answer - he was asking you to read his link.
I think you are remembering the color burst crystal @ 3.579545 MHz. That was the 1960's TV technology. 32,768 kHz came from digital watches c. 1974
I need to get me some of them 1Hz crystals! I will make building clocks a piece of cake!
You mean an MM5369 60Hz clock generator.
Not always you can take any xtal / oscillator depending what accuracy and lowed time stamp you want and more the (price performance ratio)
0.00000000001 second or 1 second or in between.
Picbuster
DickCappels
- Joined Aug 21, 2008
- 10,661
MrChips, the link appears to be broken.
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Sorry -- never heard of that one. Was it used in television sets?
Back in the '70s it was a simple way to get an accurate 60Hz time-base signal for digital clocks using a readily available crystal, the color-burst crystal. I built a communications receiver frequency counter using this part.
Oh I see, it was a chip used in conjunction with the color burst crystal. I never knew that.
DickCappels
- Joined Aug 21, 2008
- 10,661
Edit: The numbers below are incorrect.
The 3.9545 MHz crystal could be easily divided by a binary divider to obtain nearly 60 Hz (60.6606 Hz).
The 3.9545 MHz crystal could be easily divided by a binary divider to obtain nearly 60 Hz (60.6606 Hz).
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The 3.9545[Correction 3.579545] MHz crystal could be easily divided by a binary divider to obtain nearly 60 Hz (60.6606 Hz).
\(3.579545 \times 10^6 / 59659 \;=\;60.00008381\)
\(3.579545 \times 10^6 / 59660 \;=\;59.99907811\)
Factor(59660) = 2 x 2 x 5 x 19 x 157 and 59659 is prime. What divisor did you have in mind?
the closes divisors to 60.6606 Hz are 59009 and 59010.
Factor(59010) = 2 x 3 x 5 x 7 x 281 and 59009 is prime
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The output frequency with a perfect crystal is 60.00008381 Hz. This translates into a steadily accumulating error of 7.241 seconds per day (fast), so the circuit is not nearly as accurate as a crystal oscillator based on something that is a decade or binary multiple of 60 Hz.
ak
ak
