9 Dec
2007
9 Dec
'07
3:35 p.m.
On 9 Dec 2007 at 18:05, Roy J. Tellason wrote:
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...
You can probably leave out the transistor if you don't need to invert
the diode "OR". i.e. if you need to clock on the falling edge. You
could also fool with pulldowns, N.C. pushbottons, etc.
I was looking for a "valid state guaranteed" circuit where the output
terms would feed back into the input to guarantee that only one
output would ever be valid--even on powerup. You can do it, but the
gate count starts to climb rapidly as the number of states increases,
as der Mouse has illustrated.
There are diode arrays in SIPs and DIPs if you don't like the look of
discretes.
Cheers,
Chuck