6 Feb
2009
6 Feb
'09
2:38 a.m.
On Thu, 5 Feb 2009, Fred Cisin wrote:
Some of the older drives had a flywheel. A drill, in
indexing jig, a
light and photocell, any you could modify a 3.5" drive to provide 10 or 16
pulses from physically fixed positions, without being dependent on
repeatability of rotational speed.
I don't think that this would work, simply because the motor driver IC
has an internal PLL that controls the motor speed according to the output
of the flywheel sensor, and that PLL is crystal locked (a small resonator
of e.g. 981kHz, 1MHz or 493kHz). In order to change the speed you need to
change that ceramic resonator.
I know that because I've been trying to slightly reduce the speed of a
3.5" drive in order to write long tracks on an Amiga. That is BTW how I
found out that the driver IC I mentioned in an earlier post can do 600 and
720 RPM.
Christian