See previous post Discrete Logic.
EDIT: There is a flaw with this XOR circuit, see More Discrete Logic.
In my previous post I used two PNP transistors to perform of the job of XOR gate, however after building and test, the drop in voltage was too much over just a single full-adder.
Using a circuit I got from the EEV Forums, I got help when I needed to supply 14V to my OLED but the open drain on my chip supply a maximum of 2.5V, the XOR will now supply 5V from its output when it is high.
The 1k resistor represents the load. I’ve also added diodes onto the inputs since I had a problem with my AND circuit getting power from the base of the PNPs.
It requires an additional NPN and PNP transistor and a couple more resistors.