On 5/2/2014 2:45 PM, Tim Wescott wrote:
On Fri, 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?

Crank position sensors (they'll have a hall sensor and a magnet).

Laptops and flip-phones often use them to sense that the thing is closed.

Be warned that the laptop and flip-phone ones achieve very low power
consumption by only turning on about ten times a second -- at all other
times they pretty much ignore the world. Also be warned that this is the
biggest market share by far -- finding a Hall sensor that'll work on a
12000 RPM engine takes some digging (I've got part numbers, if you want
to order some from DigiKey).


Any 8 cylinder automotive electronic distributor. 8 cylinders firing
once every 2 revolutions at 6,000 rpm equals 8 times 6,000 divided by 2.

24,000 trigger events per minute. should work. Just adapt the
mechanicals, reduce, whatever, but the electronics in a distributor are
VERY robust.