Post by thread:how can I only uses 5 cpu I/O pin for 16 keyboard

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. Ten keys have two diodes each to a pair of CPU pins, there are 5c2 or 10 (= 5 x 4 / 2) such combinations. Ten more keys could have three diodes each to CPU pins (5c3 = 5 x 4 x 3 / 3 x 2 .. consider it as each *not* going to 2 CPU pins out of the five). Remember you will need a *good* debounce routine for this, it is *zero*-key rollover IOW two keys pressed simultaneously will quite possibly show as a third, different key. You will probably want to save on diodes by using all two-diode and only six three-diode key encodings, total 38 diodes. I feel it is somewhat more reliable than a single-line encoding. Of course if you allowed anywhere from one to five diodes per key, you can encode 31 keys. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A x x x x x x x x x x B x x x x x x x x x x C x x x x x x x x x x D x x x x x x x x x x E x x x x x x x x x x Frankly, I think it would be simpler and easier to use a shift register or counter... -- Cheers, Paul B.

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.

On Sun, 26 Mar 2000 09:15:59 -0800, you wrote: >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?? 4) They haven't figured out that you can almost always share pins with other functions for this type of app.