9 Dec
2007
9 Dec
'07
3:05 p.m.
On Sunday 09 December 2007 16:32, Chuck Guzis wrote:
On 9 Dec 2007 at 14:45, der Mouse wrote:
You can make your own with a pair of cross-connected transistors.
For an N-stable circuit, this technique requires
2*(N-1) inputs on each
gate. For a bistable, or even a tristable, this is tolerable; for an
8-stable, it requires eight 14-input NANDs. You could do it with
8*14=112 diodes (hmm, might need another 8) and a relatively small
handful of resistors and transistors. Doing it with just TTL would
be..somewhat inconvenient.
Perhaps something with UJTs and diodes--a UJT would give you a stable
state for each button and some steering logic would get you there.
But UJTs seem to be pretty scarce nowadays. Better to use a single RS FF per button, with reset
being driven by
the OR of all of the other buttons. You could certainly do the OR
with diodes; for an 8-button setup that would be 8 RS flip-flops and
56 diodes (fewer if you want to make a tree of them). That'd be 2
74279s or 4043s with a pile of diodes.
A similar application that comes to mind is the "game controller" where each
contestant has a push button and the first one in gets lit and locks the
other ones out. There are a bunch of circuits like that around the web. See
the "4QD" site (in the uk?) for an example of both this and the
how-to-make-your-own UJT particulars.
My initial reply on this went offlist, and I still think it's the simplest.
You take a '374 (well, I have a pile of 'em here... :-) and connect a push
button with a pullup resistor to each input. Then connect a diode to those
points too, with all of the diodes tied together. A single transistor fed
by those diodes will generate the clock...
My application for that was a multiple-battery charging setup. I still have
to finish up the design in figuring out how each select output will choose a
different circuit (different sized batteries) and build the darn thing,
saving me the effort of having to manually hook up all sorts of stuff and
deal with it.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin