[sdiy] Pressing buttons

[jhaible]

This is not trivial.
Seriously.
Ok, for 4 buttons you can do it like this:
4 RS-Flipflops, with a 3-input OR gate
(diodes ...) on each Reset input.
Button 1 is connected to SET of FF1
and to RESET (via the OR) to all other FF's.

This solves your problem - Korg did this in
the CX3 if memory serves.

BUT if you want a large number of buttons,
it becomes more difficult. Surely you don't want to
route 15 reset signals for each button to 15 OR-gates
with 15 inputs each (for a 16-button-circuit).

So the idea woud be to have *one* common RESET
line to all FFs, and one dedicated SET line from
a button to its own FF. Of course the SET must have
priority over the RESET input in each FF. This is
unusual, but possible.

Now comes the tricky part: Your Buttons produce
glitches, and your FFs have setup and hold times.
You *must* make sure that the "button's own FF"
(which gets a SET *and* RESET, while all the others
only get a RESET signal) will not fall back to reset
just the moment you release the button. You have
to make sure that SET goes *after* RESET, under
*all* conditions. Button pressed short, button pressed
long, button bouncing, buttons triggered fast after
one another. This is not trivial, and I'd like to see a solution
for this myself !

JH.



-----Ursprüngliche Nachricht-----
Von: >>>marjan<<< <urekar.m at EUnet.yu>
An: Synth-DIY <synth-diy at dropmix.xs4all.nl>
Gesendet: Sonntag, 12. Mai 2002 21:14
Betreff: [sdiy] Pressing buttons


>
> I'm in need of nice little cct, there are 4 buttons SPST,
> I need 4 outputs, when you press button#1 output#1 goes to
> logic 1 (high) all other outputs to 0, press button#2
> output #2 goes high all others to 0 and so on.
> Also output must stay high until active, not just a pulse.
> And it should be CMOS.
> I'd make it but my mind spits just sorta priority
> codec with f-fs solution, with lotsa gates. There should
> be something more elegant and simple, even inside a cmos
> chip?
>
> I know you know it!
> And no PIC solutions please :)
>
> ThanX!
>
> --
>
>
>
> marjan
>
>
> me    : Marjan Urekar
> e-mail: urekar.m at eunet.yu
> s-diy : http://surf.to/marjansystems
> music : http://go.to/forcemajeure
>
>
>