[sdiy] push button CV wanted

[Roy J. Tellason]

I have an application in mind for which I'd like the user interface to be a 
couple of push buttons,  one that would raise and the other one of which 
would lower a control voltage.  Ideally,  some sort of interlocking would 
make it do nothing if both buttons were pressed at the same time.  Any of you 
folks know of a circuit that'll do this?  Or have any ideas as to how it 
might be implemented?