Expression pedal input circuit

I’m looking to add an expression pedal input to my guitar pedal design. I have some question about how to best achieve this.

It’s my understanding that an expression pedal is basically just a passive device with a pot in it attached to a level (at least mine seems to be so). So I was thinking it would be as simple as just adding a TRS jack to my pedal, connecting GND, ring to 3v3A, and tip to one of the ADCs on the Daisy seed. However, I took at a look at the Daisy Petal schematics and I’m seeing there are some op amps involved:


Do the op amps somehow protect the seed from a short though the expression pedal, or am I missing something as to why they are necessary?

Thank you!


For the buffer for 3v3 out to the potentiometer I can see the advantage that there will be no load for this reference voltage and that no hum from long cables will be introduced.
I wonder, if a capacitor in parallel to expression_in_ext would make sense too to suppress any noise?

1 Like