To use FSR’s with the Smoothieboard, an auxiliary board is needed to interface the FSR’s to the Smoothieboard’s endstop input. Smoothieware will accept this input as if it were a simple mechanical switch.
JohnSL on Github has created such a board. It is available via AndOrNot, TriD Printing, and UltiBots. See John’s blog post about the board. This board is powered from the endstop pins. Also, see AndOrNot’s write-up on FSR’s design for a delta printer FSR pad design.
There is also a 4-point FSR controller called “Toucher” on Github suitable for square heat beds on Cartesian machines. A reference FSR mount design is published on Thingiverse.
The Deltabot group is where most discussion on using FSR’s is located. Topics to look for are: