[sdiy] interlocking switches

[Roy J. Tellason]

I *know* I've seen this in some service manual or other,  but can't remember 
where...

Say you have a row of buttons,  and you push one,  an LED lights up.  When you 
push another,  that light comes on and the first one goes out.  Sort of like 
the old mechanically-interlocked switches I remember from ages ago.

Posted about this elsewhere,  and have of course the immediate suggestion to 
throw a processor at it,  which I'm not inclined to do,  and some more that 
discuss using lots of logic.

Can any of you guys point me toward a circuit like this?  I know there were a 
fair number of commercial keyboards out there that used such stuff,  rows of 
momentary-contact switches with LEDs and some toggled on/off,  while others 
"interlocked" like I'm talking about here...