Connecting an Arduino microcontroller to Pd is no big problem: You can just put Firmata on your Arduino and use the Pduino library for communication on the Pd side. But sometimes Firmata is not the answer to every problem: You may want to turn on the built-in pull-up resistors for digital input pins, you may want to do some calculation on the Arduino before sending a message, or you may want to send a messa ...