This example is an implementation of a Morse code keyer, useful to Ham Radio CW operators using Iambic paddles (see Figure 1) to send Morse code.
CW (Morse code) is formed with DIT and DAH sounds (or, if you prefer, dots and dashes). A Dit is a short tone and a Dah is a long tone. An iambic key has two paddles. One paddle generates the Dah sound and the other the Dit sound. (In the U.S., the Dah paddle is usually the right-hand paddle.) With the assistance of a microcontroller and software like in this example, an operator, using a combination of taps and holds of these paddles, can form perfectly spaced Morse code characters.
For example, the letter B (DahDitDitDit in Morse code) is formed by tapping the Dah paddle immediately followed by a press-and-hold of the Dit paddle. Dits are repeatedly generated by the software until the operator releases the Dit paddle. Thus, with only two paddle depressions, we can generate a perfectly formed B.
This keyer example uses the generalized keyer class in the Classes directory and is documented here.

4.1 Keyer on Arduino - Wiring Diagram

Figure 2 is a Fritzing wiring diagram of the components. We have 3.5mm jack to accommodate a stereo plug for the keyer. The Dit paddle goes to pin 6 and the Dah paddle to pin 7. The buzzer is hooked to pin 13, which, on the Uno, is the pin that is hooked to the built-in, on-board LED, so when the speaker sounds, the LED also lights up.
The Arduino has built-in pull up resistors capability but we don't use it. Because not all boards have this capability, we use external resistors so that we can make a single breadboard that works across all devices.

4.2 Keyer on Arduino - Code

This is the main program for an Arduino target where we implement the Arduino-standard setup and loop functions. In setup, we create three pin objects; two for the digital inputs for the Dit and Dah paddles as well as one for the "speaker" output. (This does not really drive a speaker, rather a piezoelectric buzzer.)
Once the pin objects are created, we pass them to the keyer constructor. Because the keyer object creates a State Machine object that automatically registers the object with OOSMOS, we can then call oosmos_RunStateMachines in the loop function and the keyer state machine will be run repeatedly.

Using the portable keyer object, we can write the small bit of code specific to the PIC32 Starter Kit. The PIC32 architecture has a different way of addressing pins than does, say, an Arduino, but the pin class abstraction hides these details such that the same keyer object can be portable to all microcontrollers.
Note that the PIC32 needs to have some specialized #pragma directives to properly setup the chip. We also have to tell the run-time environment that the clock speed is 80 MHz (see line 33 of main.c).
We use the PIC32 Starter Kit board for this demo along with the I/O Expansion Board headers J10 to gain access the processor's pins. (See figure 3.) The documentation related to which pins The PIC32 does not have a setup and loop structure like the Arduino-family does. Instead, we simply implement the main function and call oosmos_RunStateMachines in a loop once all the pin and keyer objects have been created.

Using the portable keyer object, we can write the small bit of code specific to the ChipKit. Because the ChipKit is Arduino pin compatible, we can use the same pin descriptions as the Arduino example.

Using the portable keyer object, we can write the small bit of code specific to an MSP430F5529 LaunchPad board.
Fritzing does not have a part for the MSP430F5529 LaunchPad board, so we created a reasonable representation of the board's headers in order to show the connections. The pin designations for the MSP430F5529 LaunchPad board are not the same as Arduino Uno pins. (See lines 29-31.)

Using the portable keyer object and the multi-platform pin class, we can support a Windows version of the Keyer class, mostly for educational purposes.