Beep

In this exercise, we will generate a beeping sound with a 50% duty cycle, followed by a 0% duty cycle, creating a looping pattern of sound and silence. We will use the A4 note (440Hz frequency) for this. (If you're not familiar with the A4 note, please look up more information on musical notes.)

Get Top function

In the previous exercise (servo motor), we manually calculated and hardcoded the top value. In this exercise, we create a small function to calculate the top value based on the target frequency and div_int:

#![allow(unused)]
fn main() {
const fn get_top(freq: f64, div_int: u8) -> u16 {
    let result = 150_000_000. / (freq * div_int as f64);
    result as u16 - 1
}
}

div_int value

We will be using 64 as div_int.

#![allow(unused)]
fn main() {
const PWM_DIV_INT: u8 = 64;
}

Configure the GPIO 15 pin

Next, we need to configure the GPIO pin (GPIO 15) to output the PWM signal.

#![allow(unused)]
fn main() {
let pwm = &mut pwm_slices.pwm7;
pwm.enable();
pwm.set_div_int(PWM_DIV_INT);
pwm.channel_b.output_to(pins.gpio15);
}

To Set a frequency 440Hz(A4 Note)

Now we calculate the top value required to generate the 440Hz frequency (A4 note) and set it for the PWM:

#![allow(unused)]
fn main() {
let top = get_top(440., PWM_DIV_INT);
pwm.set_top(top);
}

Loop

Finally, we create a loop to alternate between a 50% duty cycle (beep) and a 0% duty cycle (silence). The loop repeats with a delay of 500 milliseconds between each change:

#![allow(unused)]
fn main() {
loop {
    pwm.channel_b.set_duty_cycle_percent(50).unwrap();
    timer.delay_ms(500);
    pwm.channel_b.set_duty_cycle(0).unwrap();
    timer.delay_ms(500);
}
}

Clone the existing project

You can clone (or refer) project I created and navigate to the beep folder.

git clone https://github.com/ImplFerris/pico2-rp-projects
cd pico2-projects/beep