An XOR may be constructed using combinatorial logic: an OR ANDed with a NAND. But can it be done with even more basic discrete components?
This circuit uses a diode-bridge and a single transistor - quite neat. It does mean however that there is no output buffer, in fact the output is powered from the inputs. I'm using an Arduino to drive the circuit and capture the output plot.
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub.