7.13. EventLoopDemo Arduino Sketch

This sketch is used by Exercise: Event-Loop Programming and Exercise: Resolution and Mapping.

7.13.1. Full Source Code

The full code is all in one file EventLoopDemo.ino.

// EventLoopDemo.ino : demonstrate generation of two simultaneous square waves at different rates

// The example program generates audio-frequency square waves at different
// pitches on pins 4 and 5 to demonstrate a simple event-loop control structure
// allowing parallel execution of two timed tasks.  The exercise asks the
// student to add an analog potentiometer input and use the input value to
// modulate the pitch by varying the waveform timing.

// Define the pin numbers on which the outputs are generated.
const int outputPin1 = 4;
const int outputPin2 = 5;

/****************************************************************/
// This function is called once after reset to initialize the program.
void setup()
{
  // Initialize the digital output pins to output drive mode.
  pinMode( outputPin1, OUTPUT );
  pinMode( outputPin2, OUTPUT );
}

/****************************************************************/
// Global variables.
long next_output_time_1 = 0;        // timestamp in microseconds for when next to update output 1
long next_output_time_2 = 0;        // timestamp in microseconds for when next to update output 2

long output_interval_1 = 500;       // interval in microseconds between output 1 updates
long output_interval_2 = 700;       // interval in microseconds between output 2 updates

int output_state_1 = LOW;           // current state of output 1
int output_state_2 = LOW;           // current state of output 2

/****************************************************************/
// This function is called repeatedly as fast as possible from within the
// built-in library to poll program events.

void loop()
{
  // read the current time in microseconds
  long now = micros();

  // Polled task 1 for output 1.  Check if the next_output_time_1 timestamp has
  // been reached; if so then update the output 1 state.
  if (now > next_output_time_1) {

    // reset the timer for the next polling point
    next_output_time_1 = now + output_interval_1;

    // toggle the output_state_1 variable
    output_state_1 = !output_state_1;

    // update output pin 1 with the new value
    digitalWrite( outputPin1, output_state_1 );
  }

  // Polled task 2 for output 2.  Check if the next_output_time_2 timestamp has
  // been reached; if so then update the output 2 state.
  if (now > next_output_time_2) {

    // reset the timer for the next polling point
    next_output_time_2 = now + output_interval_2;

    // toggle the output_state_2 variable
    output_state_2 = !output_state_2;

    // update output pin 2 with the new value
    digitalWrite( outputPin2, output_state_2 );
  }
}
/****************************************************************/