Note: This "Sending an SOS Message" activity is equivalent to the one using an LED module rather than a breadboard.

Now that we have an LED device wired to our Arduino microcontroller using a breadboard (or directly via an RGB LED module), we can send a message using light signals and Morse code. Morse code is a coding scheme used in telecommunication that encodes text characters as standardized sequences of two different signal durations called dots and dashes. The letter A, for example, is a dot followed by a dash. The chart on the left side below shows the combinations.

The Morse code rules we will use for signaling are: 

• a dot lasts for one second
• a dash last for three seconds
• the space between dots and dashes that are part of the same letter is one second
• the space between different letters is three seconds
• the space between different words is seven seconds

For an SOS ("help") message, an S is three dots, an O is three dashes, and the second S is three dots again.