Well, the circuit completely removed the noise!
The display still causes wild fluctuation in the analog POT readings though. So I put a 7805 in parallel to the incoming 9v (with some .1uf capacitors), and connected the breakout box's 5v lead to it (the button on the rotary encoder and the display are both running off of it) and it resolved the issue.
So it's quiet and stable now!
Basically I did this, using the 9v supply POS and NEG leads:
Would it be a better idea to try and solve the issue without the regulator though? Maybe an electrolytic cap between the 5v and GND buses? Or should I just stick with the 7805 and use it for just the display?
I've also been working on the display. I have it coded to show the analog POT values when turning one of them, and give an indication if the current value is above or below the currently recalled preset value. So when recalling a preset, if I want to make a fine adjustment, I can turn the knob and get visual feedback as to where the saved value is.
I plan to work on having the Digi-POTs not change value until the analog POT crosses over the currently recalled value. So if I'm doing this live on stage, it doesn't blast at 100% if I move the knob with the POT located at 100% but the recalled value is only 30% or so. This will also help protect against any electrical anomalies which may cause the POT readings to go erratic again.
