Macro Button for my Game Boy - Master button to press all buttons at once
As you have seen, if you connect all the buttons together, pressing one is like pressing them all. You can solve this with diodes:







simulate this circuit &ndash; Schematic created using CircuitLab

A, B, ... are the old buttons, and you hook your diodes directly to them or to a convenient test point. CHEAT is your new cheating button!

The diodes prevent current from flowing "back" from one point to another, while still allowing the voltage to sink low enough to trigger a logic input (roughly 0.6 volts).