I spent a considerable time searching the internet for instructions on how to build a Fender Princeton Chorus switchfoot pedal. I found this thread
which was for a Fender Princeton 112 Plus amp. However I found that it also works for a Princeton Chorus. Many thanks to the user pgcorky for posting this. It is pretty easy to build, just remember that there are specific directions for diodes as I commented on the picture. Also it is critical to use a 1/4" mono jack. Stereo jacks won't work.
Step 1: Circuit Overview Before Soldering
I tried to take a clear picture of the whole circuit before soldering. Briefly, you need to drill 3 holes in your case: 1 for the female 1/4 mono jack and 2 for the dsps switches. Then with some wires, just build the circuit.
Step 2: Pedal in Action
Now just solder all the joints, close the casing and the pedal works perfectly well. The holes are not perfectly aligned because I used a hand-drill. Perhaps I'll build a new one with a fixed drill station.