Disaster Area DMC 4 2nd Gen - rewriting firmware and expression pedals

personalnadir

Bit of a long shot, but I've replaced the firmware on my Disaster Area DMC 4 2nd Gen with one of my own making. I wanted a pedal that sends Midi CC messages instead of the default program change. I have it all working, but for the life of me I cannot get it to read any values from my Mission Engineering SP1 expression pedal. I was hoping to have it convert those to Midi CC too.

Has anyone gotten a DMC 4 Gen 2 to work with a Mission Engineering SP1 expression pedal? Looking at the internal wiring, there are only two cables coming from the TRS jack. I'm rubbish at electrics, but wouldn't a TRS jack require three wires?

The device is an Arduino Leonardo under the hood, so relatively easy to change stuff. After trying every pin though, I'm not sure whether:

a) the DMC 4 just isn't wired to take input from an SP1

b) my particular device is defective

c) I've made a basic mistake in my Arduino script

If there's someone out there who has a DMC 4 2nd Gen working with an SP1, that will eliminate a) and I can focus on b) and c). The SP1 works fine with other pedals, so don't think there is anything wrong with that.