From: "Michael Culley"
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
Subject: Re: Keypad keys per IO pin
Date: Thu, 16 Jan 2003 12:50:42 +1100
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Do'h! I've made a *huge* balls up. For 6 lines I was calculating
5x4x3x2x1=120 but I should be adding not multiplying! So it should be
5+4+3+2+1=15 which is the same as yours :-)
It is possible to double this by putting a diode on each key, although this
doesn't get as good a results as the example that was posted.
"Jonathan Kirwan" wrote in message
> On Thu, 16 Jan 2003 12:09:59 +1100, "Michael Culley"
> >Can't you just connect each key to a different combination if IO pins. eg
> >for 4 io lines:
> >Key1 Pins 1,2
> >Key2 Pins 1,3
> >Key3 Pins 1,4
> >Key4 Pins 2,3
> >Key5 Pins 2,4
> >Key6 Pins 3,4
> That is the simplex connection, in fact. See:
> (1)--o o--(2)
> |\ /|
> | o o |
> o o o o
> \ /
> o o
> | / \ |
> | / \ |
> | / \ |
> (3)--o o--(4)
> I apologize for the weird square. But it gets the point across.
> It's exactly what you are saying... connecting each key to a
> different combination of pins.
> That's a simplex.
> >If N is the number of IO lines then this gives (N-1)! keys, so for 6 pins
> >you get 120 keys
> No, you get (N^2-N)/2 switches. Not (N-1)!. Unless you are
> talking about something else and not the simplex. But your
> example appears to illustrate that you *do* mean the same thing
> I do. And if that's the case, then it is (N^2-N)/2. So the
> computation is (6^2-6)/2 = (36-6)/2 = 30/2 = 15.
> Perhaps you need to illustrate what you actually mean with 6
> I/O, if it is different. NCSRadio mentioned a web site which
> hinted at a different, binomial approach which uses diodes to
> get additional entries in the "symbol space." Nicely.