[sdiy] Pressing buttons

[cyborgzero at comcast.net]

Well, heres an idea, albeit very crude, but it has a low parts count.

A flop with edge triggered reset is required. One reset to reset the
whole chip ie all the flops.

Each switch connects to one flop input.

Each switch has its own diode, and each diode is connected to a
differentiator type pulse generator (which direction you set the diode
depends on whether the reset is pos or neg edge) , set the RC about
1ms duration. This pulse generator is connected to the global reset.

When you press, you instantly get just the edge to trigger the reset,
you hold the button for more than 1ms usually, so you press the
button, the edge trig hits the reset, all inputs go low, the reset is
deactivated in 1ms, your button is still depressed, and the data is
read into the corresponding flop.

I have used a similiar circuit for switch debouncing, but it works
equally well for this sort of thing.

Quite crude, but effective.

Stolen out of the TTL cookbook btw. ;)

With a 74175/74, you *might* be able to hook the common trig from all
the switches to the clk input, but you have the added problem of
trying to figure out how to first *clear* all the input then *clock*
the inputs to read in the button states.

This should put you on the right track.

Rob



----- Original Message -----
From: ">>>marjan<<<" <urekar.m at EUnet.yu>
To: "Synth-DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, May 12, 2002 2:14 PM
Subject: [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
>
>