[time-nuts] Got 60HZ?

Robert LaJeunesse rlajeunesse at sbcglobal.net
Fri Dec 10 17:35:11 UTC 2010


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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