[sdiy] [SDIY] First switgh detector

[bill bigrig]

Howdy,

 On tha V-tech talking tablet, there is a bend out there that uses 2 rotary switches to select the letter/number button being "pushed", i.e. the one to mangle). Is there a way, other than cascading a bunch if XOR gates to give real time control of which button is being pushed? There is no FSK or such, just a 6x7 matrix. One button rotary switch for one, one for the other. Is there not a Cmos way to detect the first button pushed and ignore all others until that buttton is released? I'd like to work with the circuit bends without having to pre-select the digit with switches, but, push any button and have the 'Glitch" work on the button that is currently being held down. Thanx.
Rig