3PDT optical true bypass PCB , eagle file and gerbers Ignore the 4pdt name files. these are an older name and file. they are working and slightly bigger pcb for the buffered version smd parts are voltage smoothing and current liminter for the LED. the main current limiter is the trim pot for adjusting the brightness 2 LED footprints for top and side mounted options. you can use both. but why? optocoupler is a TLP222A or TLP222G. cheap low cost ones will work and most have the same pinout.