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Aucbvax.2461 fa.works utzoo!decvax!ucbvax!works Wed Jul 29 17:27:44 1981 Mouse Guts >From OLSON@DEC-MARLBORO Wed Jul 29 17:19:06 1981 Conglomeration of responses to "How does a mouse work?":

Currently, a mouse is a small box with a fairly large (1-2 cm diam.) ball bearing captivated so a fraction of it lies outside the bottom of the box. As the box is rolled around, two wheels positioned perpendicular to one another pick off the rotational motion of the ball in their plane only (they slip in all other planes). Hence we get two rotational motions, one for each component of the two-dimensional motion of the mouse.

The direction and (over time) speed of the rotation shafts are measured by disks attached to the shafts encoded with a gray code, and read either photoelectrically (via led and phototran- sistor) or mechanically (via brushes). The grey code output might look like 00 01 11 10 00 going one way and 00 10 11 01 00 going the other, so we can tell the difference in direction.

Some historical information about mice, according to Bill Barns:

The mouse as originally invented by Doug Engelbart and Bill English and patented by them (rights assigned to their employer at the time, Stanford Research Institute (now SRI International)) consists of two high precision potentiometers connected mechan- ically to metal wheels with rather sharp edges, approximately 2 inches in diameter, and set at right angles to each other as close as possible without touching. [This seems a kludgey way to get this motion, because the pots would "pin" occasionally, even if they were 20-or-more-turn.] The pots are mounted on a metal base plate to which is attached a bracket. On the bracket there are (in the original, and still popular configuration) three switches which are triggered by buttons about 5/16 inch diameter [8 mm] which rest upon spring metal fingers attached also to the bracket. The bottom of the metal finger rests on the momentary-contact actuator of the microswitch. This arrangement puts some "click" into the feel. The switches typically are SPST with a common ground so that for a three button mouse there are four wires for the switches and one wire for the non-ground side of each pot - 6 total. The mouse wheel voltages are fed into an analog->digital converter of about 10 to 12 bit resolution and at appropriate times, some logic samples the digital value and does the appropriate thing.

Engelbart lives on at Tymshare, and English went to Xerox PARC and gave birth to Alto etc., (not sure if he's still there). Bill estimates the invention of the mouse between 1962 and 1967, and *guesses* 1963/4.

By the way, I got several warnings about suits, patents that I musn't breach, etc, which I condense below:

Patents to SRI and Xerox apply to a number of features of the design. The Englebart/English Patent is probably still in force, and it covers both digital and analog mice. [I was warned to check the patents before building my own. I really don't think that building your own personal whatever falls under patent laws (unless possibly if you sell it).]

Thanks to Jerry Farrell (Farrell at PARC-MAXC), Bill Barns (Barns at OFFICE), Craig Everhart (Craig Everhart at CMU-10A), and Steven Kirsck (SK at MIT-MC).

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