Keyboard scanner hints

[jhaible]

> Now, if we want to get REAL clever, we can add velocity sensing in BOTH
key
> down & key up. How??
> What you do is have 2 bussbars: one common for keys UP and 1 common for
keys
> DOWN. Then you
> attach BOTH busbars to ground!!! So, what happens is that the "addressed"
> keys start by reading a '1',
> then they read a '0' AS THEY ARE TRAVELLING BETWEEN BUSBARS, then they
read
> a '1' again!!!
> So, all your uP or circuitry has to do is TIME how long it read a '0' for
> each key. Of course, you have to
> assume that on power-up initialization, you don't freak out the logic by
> HOLDING KEYS DOWN!! That of
> course will read the scans 'backwards' for velocity.

But what if one key is not completely pressed down, and then released again
??
Why not use the scanner to *feed* a "high" into the keys, one by one, and
then
use the two bus bars to *read out* the value ?

JH.