  Alternative computing approaches that interface readily with physical systems
are well suited for embedded control of those systems. We demonstrate finite
state machines implemented as pneumatic circuits of microfluidic valves, and we
employ these controllers to direct microfluidic liquid handling procedures such
as serial dilution on the same chip. These monolithic integrated systems
require only power to be supplied externally, in the form of a vacuum source.
User input can be provided directly to the chip by covering pneumatic ports
with a finger. State machines with up to four bits of state memory are
demonstrated, and next-state combinational logic can be fully reprogrammed by
changing the hole-punch pattern on a membrane in the chip. These pneumatic
computers demonstrate a new framework for the embedded control of physical
systems.
