Firmata protocol library for common lisp.

Turn on and off an LED on your arduino:

(with-firmata-io "/dev/cu.usbmodem1411"
                 (digital-write 13 (cmd :on))
                 (sleep 2)
                 (digital-write 13 (cmd :off))
                 (cl-async:exit-event-loop))

Note that the with-firmata-io macro runs the body forms within a cl-async event loop, so you can use all its functionality there, but at the moment you need to exit manually or it will wait forever.