On 02 May 2014 14:54:05 -0300, Mike Spencer
wrote:


Tim Wescott writes:

On Thu, 01 May 2014 23:55:27 -0300, Mike Spencer wrote:

[snip]

Take apart an old (computer) mouse and get the LED and sensor. Should
be far more responsive than a reed switch. (But I'm only guessing.
Electronics weenies to the bridge, please. Is there such a thing as a
high-speed, solid state magnetic switch?)

Yes there is -- they're called Hall switches, or Hall sensors (they work
by the Hall effect. You get one guess as to the last name of the guy who
wrote it up first.)

Ah, tnx for that. Heard of "Hall effect", didn't know that commonplace
articles implemented it. Where would I look in old junk to find one?

I just don't feel that doing this optically will be robust.

Someone gave me a DecWriter II in 1990, when it was at
archaeological-artifact stage of life, which I played with for a
while. The opto-mechanical unit for spacing eventually failed and I
was never able to get it working again. I suppose the similar little
wheels in a mouse would have the same potential for refractory
NFG-ness, which is why I thought of but didn't try that for my (real)
mouse tach.
An old Omni distributor generally had 2 of them. (Aries and reliant
too)