[time-nuts] Got 60HZ?

[Javier Herrero]

It seems that we're all trying to find the most obstuse way to obtain 
60Hz from 10MHz since the division is not integer... why not simply 
multiply the 10MHz input signal by 3 and feed the resulting 30MHz signal 
to any suitable divider by 500000 chain? the result will be nice, 
spectrally pure and even 50.000% duty cycle :).

A PLL multiplication solution could be to fed the 10MHz signal to any 
microcontroller that uses an internal PLL to obtain the internal clock 
(like an AT91SAM7S32, but there are a zillion of similar ones), get a 
30, 45 or 60MHz internal clock, and obtain the 60Hz from a timer output. 
Single chip solution, and software needed only for register 
initialization (not so spectrally pure since the internal VCO of a 
microcontroller is not best class in the world)

Regards,

Javier

El 10/12/2010 18:35, Robert LaJeunesse escribió:
> FWIW...
>
> While any small micro can somehow get to 60Hz from 10MHz the Cypress PSoC has
> some unique features that might make it advantageous for certain applications.
> It has multiple programmable analog and digital blocks as well as a useful 8-bit
> micro. Here's what I'd consider for the job, all done for a few bucks in a
> single CY8C24x23 part:
>
> In a digital block, take the 10.000000MHz input, divide it by 305 to get
> 32786.88... Hz and route to output pin.
> (Might need to use an analog block as a [self-adjusting?] DC bias output so the
> 10MHz source signal can be AC coupled.)
> Loop the 32786.88... Hz back to the "32768" crystal input, and use the internal
> clock PLL of 732x to get exactly 24.000000 MHz.
> Use digital blocks to divide the 24MHz by 200000 and then 2 to get an exact
> 60.000Hz square wave, locked to the 10MHz source.
> (One could use 240000 and then 2 to get an exact 50.000Hz - the hard way!)
>
> There's still lots in even a minimal PSoC that isn't allocated and can
> definitely do something useful. For example take the 24MHz clock and run a
> software DDS on the micro, feed the DDS via a sine lookup table to an analog
> block DAC, bring that out and loop it through a (continuous time) analog block
> lowpass filter to derive a low distortion sine wave. Or tweak the lookup table
> and get any waveshape reasonable, like triangle or sawtooth. Sync the DDS to the
> 60Hz if need be, although it might marginally add to sine wave distortion /
> jitter.
>
> One chip and some passives, no crystal, 10MHz in, exactly 60Hz out, not the
> lowest jitter, but definitely precise. And with a little work get low a
> distortion sine, triangle or sawtooth output to boot.
>
> Regards,
>
> Bob L.
>
> p.s. No, I have no relationship with Cypress, I just like the PSoC family. Maybe
> because I'm an old analog guy at heart, and since small micros seem to rule the
> roost may as well pick one that leans the most in my favored direction.
>
>
>
> ________________________________
> From: Bob Camp<lists at rtty.us>
> To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
> Sent: Fri, December 10, 2010 7:32:03 AM
> Subject: Re: [time-nuts] Got 60HZ?
>
> Hi
>
> Easier to do with a cheap pic.
>
> If all you want is 60 Hz of of a 10 MHz source, load up one of the timers /
> PWM's. Change the load as required to hit 60 Hz. Might be<10 lines of code,
> certainly not over a couple dozen.
>
>
> Bob
>
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-- 
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Javier Herrero                            EMAIL: jherrero at hvsistemas.com
Chief Technology Officer
HV Sistemas S.L.                          PHONE:         +34 949 336 806
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