saturable inductor

[Rich Grise]

My favorite old keyboard (it was a Burroughs, which should give a hint of
its age) had keyswitches that moved a small magnet to saturate a core,
which had two one-turn windings (looked like staples), one to excite and
one to sense. It had great key feel...no mechanical damping or hysteresis
like a buckling switch. Hall switches exist, too, but this was ...
elegant.

I once bought a raw keyboard at some surplus outfit - it was about 64 keys
with an SPST switch for each; the switches were waay kewl - it had sets
of quadfurcated contacts facing each other, but with a little plastic
baffle molded into the key.

v----plastic thing
_
| |
contacts \ | | /
\| |/
/| |\
/ |_| \
| |
| |
| |

When you pressed the key, the baffle went down, wiping the contacts
and letting their spring force push them together.

I hand-wired a matrix, drove it with a 6502, and used it on my Z-80
TV typewriter. ;-)

Cheers!
Rich