d. External switch

How to add external switch (tact switch) , as many times OSD is hidden inside of plane so access for button is limited .

This button (switch) is working between processor's pin and GND - so easiest way is to solder cable to button "hot pin" and simply switch it to GND for button proper work .

Or if we want made an removable switch , here is picture how to add reset button from old PC case, working as external button . Connection is simple , we use an unused pin connected to "hot" pin of button .