On 4/22/19 7:39 AM, David Gesswein via vcf-midatlantic wrote:
Some drives (Apple Widget, Plus Hardcard / Quantum) had a fine position sensor on the head arm. The Lisa disk uses this during a low level format.
Found picture of the drives online. Looks like they used an optical position sensor similar to how my RK05's work. This was probably the last gasp of that method before the track density got too high for it to work.
Are you saying the Widget only uses it to format? How does it determine head position during normal operation? For my RK05 its always uses the optical sensor for positioning the heads.
It's only for relative position; the quadrature approach cannot "unwrap" the phase. The drive logic must have a general idea of where the heads are, by counting the sine/cosine phase wraps as they cross 0 degrees as the head carriage moves. -Dave -- Dave McGuire, AK4HZ New Kensington, PA