[sdiy] 440hz revisted

[Magnus Danielson]

From: Tom Arnold <xyzzy at sysabend.org>
Subject: [sdiy] 440hz revisted
Date: Wed, 11 Jan 2006 04:16:55 -0800
Message-ID: <20060111121655.GH10396 at moo.sysabend.org>

> In a fit of narrowmindedness earlier today I was quite fixated on a 4.400mhz
> crystal however after Paul S mentioned that getting one divisible by a power
> of 2 would be a better idea, I started considering other options.

> Seems like a better idea is a standard cheap colourburst crystal like
> everyone else seems to use, and pull it the 500hz required to divide it
> cleanly.  No, it wont be power of 2 compatible, but it will be 25cents each
> and sealed in a metal box away from air currents and fast temperature
> variations it should be stable enough that after dividing the drift wont be
> noticable.


Well,

      455*525*30
f   = ---------- = 3579545,454545... Hz
 SC    2 * 1.001

f  = 8192 * 440 = 3604480 Hz
 0

f  - f   = 24934,545454... Hz
 0    SC

That would be about 3 Hz below and you need to pull some 20k before getting it
even risking sharp.

A 4,4 MHz oscillator divided by 625 followed by a 7-stage binary counter would
supply A1, A2, A3, A4, A5, A6, A7, A8. Simple enought.

Cheers,
Magnus