[sdiy] A440 -- almost

[Colin f]

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl 
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Scott 
> Gravenhorst
> Sent: 19 October 2002 1:58
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] A440 -- almost
> 

> >In this first post, thought I'd share some quick notes on the A-440 
> >reference frequency or calibrator thread that came up recently.
> >
> >I discovered that the NTSC color burst reference frequency 
> is very close 
> >to a necessary superharmonic. 3.579545 MHz / 8134 yields 
> 440.07192 Hz.
> 
> The prime factors of 8134 are 2, 7, & 83 with 7 used twice.  Ugh.

I'd use the 3.57MHz xtal to clock a PIC 12c508.
Set up the PIC internal counter to count to 4067, and toggle an output
pin every clock overflow.
440Hz square wave.
That'd be half a dozen components, and cost 2 or 3 bux.
Plus you could have switches on other input pins to select different
tuning pitches if required.
Or you could add the old crow's shift register noise generator code, and
have a switchable tuning reference/noise source.
Of course, you'd need to be able to program the PIC...

Colin f