Re: Write Signal on Disk II Question

[Alex Freed <alexf@mirrow.com>]

Bryan Parkoff wrote:
>     I have no idea how narrow or wide between clock bit on depending of 
> rotation speed.
>
> For Example:   "_" is zero bit.  "1" is 1 bit.
>
> ___1____1________1____1____  280 RPM
> _____1______1__________1______1______  300 RPM
> _______1________1____________1________1________  320 RPM

A little elementary school level math and a calculator can help :)
If the nominal delay between consecutive 1 bits is 4 uS at 300 RPM,
it will be 4 * 300 / 280 =~ 4.29 uS
and 4 * 300 / 320 = 3.75 uS at 320 RPM

So after you detect a 1 bit, see if there is another pulse in the 
interval from 3.75 to 4.3 uS. So sampling at 2 MHz will not get you
a full resolution. 4 MHz is much better: you can sample at 3.75, 4.0
and 4.25 uS.

-Alex.