Hi, Bohan,

Thanks for your reply.  Yes, I’m trying to built an expression/footswitch pedal on my own because I don’t need that bulky wah-wah-style pedal and don’t need to operate the expression control like I do on a wah pedal.

You should wire tip to expression pedal and ring to your aux switch. You also need to set H9’s EXP PDL setting to [EXP+AUX].

Thank you!  So, my initial schematics seems to work!