9 Dec
2007
9 Dec
'07
1:32 p.m.
On 9 Dec 2007 at 14:45, der Mouse wrote:
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.
Cheers,
Chuck