Summary of Arduino Sketch Event Loop Demo
This Arduino sketch, named "EventLoopDemo," demonstrates generating two simultaneous audio-frequency square waves at different rates on pins 4 and 5. It uses a simple event-loop structure to allow parallel execution of two timed tasks, toggling the outputs based on microsecond timing intervals. The exercise encourages adding an analog potentiometer input to modulate the pitch by adjusting the waveform timing. The program initializes output pins and repeatedly checks timing to update the output states, producing square waves without blocking code execution.
Parts used in the EventLoopDemo:
- Arduino microcontroller board
- Two output pins (digital pins 4 and 5)
- Analog potentiometer (optional, for pitch modulation)
This sketch is used by Exercise: Event-Loop Programming.
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 );
}
}
/****************************************************************/Source: Arduino Sketch Event Loop Demo
