Using transistors to replace push buttons
Your circuit forces 5-0.6 = 4.4V onto the end of R, regardless of which switch is used.

To work you need a high value R in series with the base, and better to have emitter to gnd, and R to collector. An N-fet would be easier, but still has to be S to gnd







simulate this circuit &ndash; Schematic created using CircuitLab

Bipolars will always be adding current/switching voltage, and making the apparent resistance wrong.

Cmos transmission gates are best for this job. 74HC4066. 

As an add on, you can connect them to the circuit directly in place of switches, or across existing switches, without re-wiring the resistors, and without regard to polarity, multiplexing arrangements etc.

You can also use them for logic functions e.g in series to get the AND function i.e. the 4th one is in series with LCD_CTRL and controlled by _Mode. 







simulate this circuit