6 Feb
2014
6 Feb
'14
12:44 p.m.
This one is the same - magnet on the plunger, but just
a ferrite on the
key base.
Posibly even the asme part as HP used. I don't think HP made them
themselves.
As I mentioned, HP had a few wiht 2 ferrites and 3 loops of wire. In the
up state, both ferrites were saturated by the magnet. When you pressed the
eky, it moved the magent far enough from the upper ferrite to allow it to
couple the 2 loop,s but the lower one rmained saturated. Press the key
hard and rthe magnet was moved dwon far enough to allow both ferrites
top[ couple their respective loops. This was used for the 4
cursor-movement keys in the hP9845, which auto-rpeat if pressed hard.
I noticed -- but I have Nd magnets in stock from a 3D
printing project
(and some smaller ones from an aborted micro-actuator project), anything
else I'd have to order in.
You mean you don't have a box of assorted magnets?
The circuitry that HP used should be in
'my' HP9845B schematics. From
what I rmmemebb the actual key drive/sense circuitry doesn't involve any
custom or hard-to-find parts. There is a single-chip keyboard encoder,
but you wouldn't need that if you were jsut making one key as a
demonstration.
I'll see if there are any schematics floating around... otherwise a
simple description will likely be enough to reproduce it.