Apologies if I did not give enough information. I want to connect a eurorack modular synthesizer to an Arduino. Synth runs off a 12v bi polar PSU. Outputs an average 10vpp and is used as a control voltage for the Arduino analog input. The synthesizer also has a 5v pulse output from a sequencer to use as a trigger. However, this 5v is not always garaunteed. Sometimes it can be up to 10v from certain modules in the synth. This will also be going into the Arduino.
So if opto isolation only gives a square wave. I should use this on the trigger input from the synth. And use a voltage divider current resistor on the control voltage input?
If I used opto on the control voltage input. Would it still produce 0-5v. Or just a 5v square? The control voltage varies in a stepped manner. (Switching between 8 outputs)?
Would the fact the opto is a square output make this stepped control vintage more stable?