I have to wonder sometimes when someone asks this type of question.

1) Are they just sooooo new that they don't know what kind of trouble they
are getting themself into?

2) They have LOTS of diodes laying around and too broke to afford the IC's?

3) They want us to do their homework for them??

"Paul B. Webster VK2BZC" wrote:

> Wing Kent Kwan appears to have written:
>
> > how can I only uses 5 cpu I/O pin for 16 keyborad keys input?
> >  My means is No use IC to do it!
> >  only use the diodes to do it? but I don't know how to connected it?
>
>   Fairly simple.  Each key goes to ground, each CPU line has a pull-up.
> Each diode in the matrix goes anode to CPU pin, cathode to key.