I just finished a DIY version of it:
You need to wire up the A5 analog pin [ed: fixed] of the Arduino to the touch plate, and then connect the bit to ground. I took a pair of audio jacks, wired up pin 5 and ground to one of them, and connected the other one to the touch plate and an alligator clip.
From there, you can use the “Touch Plate” feature in Chilipeppr, all you need to do is enter in your plate thickness, and hit “Run”. You can see in the video that after I zero it out, I remove the plate and tell it to go to zero on the Z axis, and it comes right down to the exact top of the work surface.