Often the question is asked, what is the simplest way to get modular synth control voltage (CV) into an analog input pin?
This simple circuit using only 3 resistors and 1 capacitor converts the -5V to +5V CV signal range to the 0 to 1.2V ADC input range.
For Teensy 3.2, 3.5 and 3.6, you would use analogReference(INTERNAL) to configure for the 0 to 1.2V range. Then you can read the CV signal at any time with analogRead().
While this circuit is the simplest and easiest way, it is not necessarily the best way. The input impedance, or load placed on the CV signal, it 31K ohms, rather than the standard 100K impedance normally used for modular synthesis systems. This forum discussion goes into the circuit’s limitations and suggests more advanced ways using opamps.
Originally this article was published on the DorkbotPDX website. Since that time, the DorkbotPDX blog section has vanished. I’m reposting it here, to preserve this info. A copy of the original can also be found at the internet archive.