I'm looking for a little help designing a transistor circuit. I have a small LCD (I took from an after-market car backup cam system), and I’m trying to control its built-in menu using the buttons of an old handheld game system. The LCD has 3 buttons to navigate its menus which are on a separate PCB with a single 3.3V signal line. The way it works is each button shorts the line to ground through a different resistor.
My idea was to just rebuild that circuit and replace the buttons with NPN transistors, then connect the base of each transistor to the output of a logic gate, which would detect when two of the game system’s buttons were pressed simultaneously.
The problem I seem to be having is the transistors aren't being triggered, and I don't really know enough about them to know if I've designed this wrong (the logic gate seems to be outputting correctly, so I must have done something wrong with the transistors).
The parts I’m using: