[sdiy] Keyboard scanning rate

[David G. Dixon]

> I know there are a few people on the list who have designed and built
> their own scanned digital keyboards, so I'm hoping for some differing
> opinions.

I did a custom version of the MFOS scanning circuit for my keyboards.  It's
simple monophonic, no velocity/pressure sensing, etc.  The clock is a
schmitt trigger RC oscillator built from a 74HC14, with R = 100k and C =
100pF, or RC = 10us.  Hence, the frequency should be about f = 1.25/RC =
125kHz.  My system is 7 bits, so the count is 0 to 127, which means that the
keyboard is scanned 1000 times per second.

It seems instantaneous, obviously.