Ground Terminal Usage in Push Button Circuits

Hoping that only one button will be pressed at a time, I have a software solution based on polling :

Let A is connected to Pin1, B is connected to Pin2 and so on..

First configure Pin1 as output port and all others as inputs. And out a logic '1' at Pin1. Read the values at Pin2 to Pin6.

• if Pin2 = '1' then SW1 is pressed.
• if Pin4 = '1' and then SW5 is pressed.

Now repeat the above steps with Pin2 as output port and others as input ports (Change the conditions accordingly).

EDIT: As Spehro Pefhany commented, this will work for upto two switches pressed simultaneously.

Additional switching doesn't seem necessary.

Just receive all four buttons on your PCB, then implement the modalities in software/firmware:

A | B | C | D <-- Buttons (0=pressed, 1=open)
-------------
1 | 1 | 1 | 1 <-- Nothing pressed (idle)
0 | 1 | 1 | 1 <-- Button A
1 | 0 | 1 | 1 <-- Button B
1 | 1 | 0 | 1 <-- Button C
0 | 1 | 1 | 0 <-- Button Shift-A
1 | 0 | 1 | 0 <-- Button Shift-B
1 | 1 | 0 | 0 <-- Button Shift-C

Using solid-state switching (or a relay) will increase the number of outputs relative to the inputs. If you have a system with only 4 button inputs (because it was designed to work with 4 button controllers) where will you connect the extra signals you generated?

If your original system was designed to receive 6 buttons, but you only have 4 buttons, then you can use either the firmware approach suggested or a decoder solution (for example 74LS148) to implement the 4 -> 6 transformation.

If you'd like additional details on this approach please provide more information about what you are connecting the modified controller to and I'll elaborate appropriately.