[time-nuts] Got 60HZ?

Chris Albertson albertson.chris at gmail.com
Thu Dec 9 17:14:31 UTC 2010


What you are doing is "dithering".  That is the "Leap Count".  There is a better
way that gives you the exact solution.     If you think about it, what is the
computer doing between counts? nothing really.   Put that time to use.
Why not measure the the 1Khz period.  Or measure the period of the last
1000 counts.  then toggle the output at 60/1000 of that period.  This is a
"software phase lock loop" .   Another way to think about this is to think what
would you do if your frqency reference was a one pulse per second "tick".

About how to "square" a wave.    Some people suggest amplifying the sine wave
then feeding it to a 74xxx series logic gate.  There is no need to amplify.
What you do is compare the sine wave to zero.  All sine waves of any amplitude
even if it is .1 Volt or 100 Volt peak to peak, they all cross zero so
you flip the square
wave each the sine wave crosses zero.  But do it with a "Schidt trigger".
This is a very noise immune circuit.  Place
the gard bands at -0.1V and +0.1V and it will work with any sine wave,
no amplifier
required.   Also you can build it with an 8 pin dip chip, no need for
a 14 pin chip.

See here for more on this.
http://en.wikipedia.org/wiki/Schmitt_trigger


On Wed, Dec 8, 2010 at 8:13 PM, Michael Poulos <poulosmd at gmail.com> wrote:
> Recently I bought a Efratom Ru frequency standard from eBay and a frequency
> divider chip that makes 1MHZ,100KHZ,25KHZ,10KHZ,100HZ and a 1HZ output.
> Today I thought of a way to make a nice 60HZ so you can use a mains-powered
> clock for the display (using amplifier and transformer wired "backwards").


-- 
=====
Chris Albertson
Redondo Beach, California



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