teensy as a keybooard throws error as keyboard input I have a program (bash script) I wrote that is for stop motion animation. The script works perfectly, when I use any given keyboard on my laptop, and it works on other computers, as well.  So i wanted to add a controller, using a teensy, and the keyboard library. source here:

The teensy, set up as a keyboard, using one of the example codes, which I modified. The output appears correct: when I press any of the buttons, I get the expected output (asdw). But, the script throws an error, and exits anyhow, which means something else is being sent besides the key presses I desire.

So, WHY?
Here is the keyboard source for the teensy:

 /* Buttons to USB Keyboard Example

   You must select Keyboard from the "Tools &gt; USB Type" menu

   This example code is in the public domain.
*/

#include &lt;Bounce.h&gt;

// Create Bounce objects for each button.  The Bounce object
// automatically deals with contact chatter or "bounce", and
// it makes detecting changes very simple.
Bounce button0 = Bounce(0, 10);
Bounce button1 = Bounce(1, 10);  // 10 = 10 ms debounce time
Bounce button2 = Bounce(2, 10);  // which is appropriate for
Bounce button3 = Bounce(3, 10);  // most mechanical pushbuttons
Bounce button4 = Bounce(4, 10);
Bounce button5 = Bounce(5, 10);  // if a button is too "sensitive"
Bounce button6 = Bounce(6, 10);  // to rapid touch, you can
Bounce button7 = Bounce(7, 10);  // increase this time.
Bounce button8 = Bounce(8, 10);
Bounce button9 = Bounce(9, 10);

void setup() {
  pinMode(0, INPUT_PULLUP);
  pinMode(1, INPUT_PULLUP);
  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
  pinMode(4, INPUT_PULLUP);
  pinMode(5, INPUT_PULLUP);
  pinMode(6, INPUT_PULLUP);  // Teensy++ LED, may need 1k resistor pullup
  pinMode(7, INPUT_PULLUP);
  pinMode(8, INPUT_PULLUP);
  pinMode(9, INPUT_PULLUP);
}

void loop() {
  // Update all the buttons.  There should not be any long
  // delays in loop(), so this runs repetitively at a rate
  // faster than the buttons could be pressed and released.
  button0.update();
  button1.update();
  button2.update();
  button3.update();
  button4.update();
  button5.update();
  button6.update();
  button7.update();
  button8.update();
  button9.update();

  // Check each button for "falling" edge.
  // Type a message on the Keyboard when each button presses
  // Update the Joystick buttons only upon changes.
  // falling = high (not pressed - voltage from pullup resistor)
  //           to low (pressed - button connects pin to ground)
  if (button0.fallingEdge()) {
    Keyboard.println("s");
  }
  if (button1.fallingEdge()) {
    Keyboard.println("d");
  }
  if (button2.fallingEdge()) {
    Keyboard.println("w");
  }
  if (button3.fallingEdge()) {
    Keyboard.println("a");
  }
}


What should I do to just get the key presses (asdw) from the teensy as if it were a plain old keyboard.
You are calling Keyboard.println() which sends the character string followed by a new line.  If you want to emulate a keyboard you should only use Keyboard.print() which only sends the character string with no new line.