Added Arduino .ino file to src directory

src/operant_serial/operant_serial.ino

@@ -0,0 +1,61 @@
+
+int baudRate = 19200; // 9600 seems common though it can probably be increased significantly if needed.
+char ioBytes[2];
+int ioPort = 0;
+
+void setup()
+{
+  // start serial port at the specified baud rate
+  Serial.begin(baudRate);
+  while (!Serial) {
+    ; // wait for serial port to connect. Needed for Leonardo only
+  }
+  Serial.println("Initialized!");
+}
+
+void loop()
+{
+  // All serial communications should be two bytes long
+  // The first byte specifies the port to act on
+  // The second byte specifies the action to take
+  // The actions are:
+  // 0: Read the specified input
+  // 1: Write the specified output to HIGH
+  // 2: Write the specified output to LOW
+  // 3: Set the specified pin to OUTPUT
+  // 4: Set the specified pin to INPUT
+  // 5: Set the specified pin to INPUT_PULLUP
+  // if we get a valid serial message, read the request:
+  if (Serial.available() >= 2) {
+    // get incoming two bytes:
+    Serial.readBytes(ioBytes, 2);
+    //Serial.println("I received: ");
+    //Serial.println(ioBytes[0], DEC);
+    //Serial.println(ioBytes[1], DEC);
+    // Extract the specified port
+    ioPort = (int) ioBytes[0];
+    // Switch case on the specified action
+    switch ((int) ioBytes[1]) {
+      case 0: // Read an input
+        Serial.write(digitalRead(ioPort));
+        break;
+      case 1: // Write an output to HIGH
+        digitalWrite(ioPort, HIGH);       
+        break;
+      case 2: // Write an output to LOW
+        digitalWrite(ioPort, LOW);        
+        break;
+      case 3: // Set a pin to OUTPUT
+        pinMode(ioPort, OUTPUT);
+        digitalWrite(ioPort, LOW);
+        break;
+      case 4: // Set a pin to INPUT
+        pinMode(ioPort, INPUT);
+        break;
+      case 5: // Set a pin to INPUT_PULLUP
+        pinMode(ioPort, INPUT_PULLUP);
+        break;
+    }
+  }
+  //delay(10); // Should probably move to a non-delay based spacing.
+}