On Tuesday 31 August 2004 01:39 am, ben_englund wrote:
> > Could you elaborate as to how..... Especially in a
> > power down condition where upon one could loose track.
> > I take it, there is some trick, as many devices, use
> > relative rather than absolute positioning. WIthout a
> > home position to index off of, it would seem one could
> > loose the position of the pointer if it were turned
> > and power was off.... Or is it interrupt driven such
> > that the micro stays alive and wakes up should the
> > shaft be turned???
> >
> > Ron
>
> Maybe do like was already stated earlier and just use LEDs around the
> dial to indicate position. Then don't put any position indicators on
> the dial itself. Then when you turn the unit on, you could have it
> start in the "home" position no matter how much the dial itself has
> moved while off.
Just like a mouse pointer starts in the middle of a screen.
> Or you could use a bunch of reed switches mounted in a circle and a
> magnet mounted to a disc on the shaft, but I'm sure that would be
> pretty pricy.
Radio Shack used to sell a bundle of those for a fairly low price, as I
recall.
> I've heard that green LEDs can act as photodetectors. They are cheap
> if you could get them to work. Then just put a bunch in a circle a
> detectors and one on a disc on the shaft as an emitter. Anybody have
> any luck using LEDs as detectors?
I've never tried this, never saw the need. If you want some cheap (free?)
photodetctors and emitters, take any trashed floppy drive (that people would
normally just throw away) and grab the sensors out of it. Some will use a
mechanical switch for the ones along the edge of the disk package, some will
use optical parts, but almost all that I can figure will use an optical pair
for the index sensor, so you get at least one. There can be as many as four
pairs in there (disk type, write protect, index, and home position). Or take
apart a dead mouse, there will be at least four pairs of sensors in there...