Grumpy_Mike:
A 7805 is not a transistor it is a voltage regulator. You must use them with a capacitor on the input and the output.
Thanks .... I knew it was a voltage regulator, but mistakenly thought it was a transistor.
I tried using one with a .1uf ceramic capacitor at the output and a .047uf ceramic at the input, but I still get the fluctuation in the 5v reference signal when the display is connected.
I know the .047uf value one should be .33uf, but I had these caps left over from a previous project so gave it a shot. I have some .22uf electrolytic caps here too. Should I try placing one in parallel to the output?
The rest of the components for the power supply Allan recommended will be here today, so maybe this testing is all a moot point anyway ... although I am learning quite a bit through the process.