Please help me out with this circuit

[mocuZ]

Thanks
I figured out the RESET part: I am using 20 buttons. So 4 are free. I'll just use one of
them to do the start combination: 1->1, 2->2, 3->3, 4->4. And whenever I want to
back to "straight-trough" mode I'll just bush that button.

 

[ericgibbs]

Thanks
I figured out the RESET part: I am using 20 buttons. So 4 are free. I'll just use one of
them to do the start combination: 1->1, 2->2, 3->3, 4->4. And whenever I want to
back to "straight-trough" mode I'll just bush that button.

hi,
You could use a switch on the LS30 spare input pins. A pull up resistor, say 10K to +5V, use the RESET switch to pull the pin low.