Stupid Arduino Tricks: Morse Code
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This project served as an introduction to Arduino programming with minimal hardware investment.
Executing this sketch, the Arduino will accept serial data over the USB port, and convert the
Morse-legal characters into Morse code on the LED attached to digital pin 13. It will ignore any
non-Morse legal characters in the serial stream.
In the other direction, the Arduino will decode Morse code keyed in via a button switch attached
to digital pin 2 into ASCII text that is transmitted as serial data over the USB port.
Hardware
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Some hard-to-read ASCII art of the Arduino board pinouts:
Arduino
------+
2|------|SW1|----|GND|
3|------|LED|----|GND|
13|------|LED|----|GND|
------+
GND = Ground
LED = Light Emitting Diode.
SW1 = Button switch, nominally OFF.
The switch on pin 2 can be attached directly to ground because the 328 has a built-in pull-up
resistor on it. The software just has to remember to turn the pin on when configuring it. Notice
that keying the switch will pull pin 2 to ground, so a LOW signal represents keying, and a HIGH
not keying -- reverse of what you might think. Why? Because I had nominally off switches and didn't
want to buy nominally on ones. "Minimal hardware investment," remember? Also notice that there's
no debouncing hardware in the circuit. Debouncing is handled in software. "Minimal hardware
investment" again.
The LED on pin 3 is used to verify that you are keying correctly on pin 2. It will be on when the
switch is keyed, and off when it is not.
The LED on pin 13 is used to output Morse code of the ASCII received on the USB serial port.
You can use the onboard LED for this purpose, but since the RX and TX LEDs will be flashing right
next to that one, it's easier on the eyes to use an external LED.