7 May
2012
7 May
'12
12:29 p.m.
The reason is that they don't want the expense of
adding a diode in the
matrix along with each switch, to prevent the phantom keys.
I suspect it's also the physcial problem of adding all the diodes. It's
OK if the kkeyboard is separate switches soldered to a PCB, but most are
membrand devices, and it's non-trivial to add idodes to a membrane.
FWIW, I think some older HP keyboards did have a diode in series with
each swithc. I would ahve ot check the sckenatics, but off the top of my
head the older HP-HIL one (46020), the one for the Integral and the one
for the HP150 al ldid.
-tony