Control the Buzzer Sound Using Swift Language

In this project, you will get a buzzer buzzing. And its sound will change as you turn the potentiometer.

Step 1: What You Will Need

The parts you will need are all included in this Maker kit.

• SwiftIO board
• Shield
• Buzzer module
• Potentiometer module
• 4-pin cable

Step 2: The Buzzer

The buzzer could produce sound as you apply voltage to it. Inside it, there is a diaphragm that would vibrate in response to the voltage. It thus vibrates the surrounding air and generates the sound.

There are two kinds: active buzzer and passive buzzer.

• The active buzzer could produce sounds as you connect it to 3V3 since it has an internal circuit that could alternate the current.
• The passive buzzer needs a PWM signal. And if its frequency is higher, the pitch it produces would be higher.

The buzzer you are going to use is the passive one. So you need to apply a PWM signal to it.

Step 3: What Is PWM Signal

Pulse Width Modulation (PWM) can simulate analog results digitally. It is a square wave, a signal that switches between on and off. The duration of the "on-time" is called the pulse width. By changing the ratio of the on-time to the off-time, it will simulate the voltage between fully open (3.3 volts) and off (0 volts).

For example, if you repeat this switching pattern with LEDs fast enough, the signal seems to be a stable voltage between 0V and 3.3V. And the LED would show different brightness.

Now come more concepts. A fixed time period consists of on and off time. The duration or period is the inverse of the PWM frequency. For example, when the PWM frequency is 500 Hz, one period is 2 milliseconds.

The duty cycle is the percentage of on-time during one period. Its range is 0-1. 1 means the output is always on. 0 means the output is always low. And the signal with a 0.5 duty cycle is on for 50% of the time and off for 50% of the time.

Step 4: The Circuit

Place the shield on top of your SwiftIO board.

Connect the potentiometer module to pin A0 using a 4-pin cable.

Connect buzzer module to pin PWM2B (D10).

Step 5: The Code

// Import the SwiftIO library to use everything in it.
import SwiftIO

// Import the board library to use the Id of the specific board.
import SwiftIOBoard

let a0 = AnalogIn(Id.A0)

// PWM, also known as Pulse Width Modulation is a type of digital signal.
// The PWM signal can be used to configure a servo, or to control the dimming of a LED light.
// Initialize a PWM output pin.
let buzzer = PWMOut(Id.PWM2B)

while true {
    // Read the input voltage.
    let value = a0.readPercent()
    
    let frequency = Int(400 + 2000 * value) // calculate the float value into Int type to serve as frequency.
    buzzer.set(frequency: frequency, dutycycle: 0.5) // Set PWM parameters.
    sleep(ms: 20) // Set the duration of the notes.
}

Step 6: Code Analysis

import SwiftIO
import SwiftIOBoard

First, import the necessary libraries for this project: SwiftIO and SwiftIOBoard. SwiftIO is used to control the input and output of the SwiftIO board. SwiftIOBoard defines the pin name of the board.

let a0 = AnalogIn(Id.A0)
let buzzer = PWMOut(Id.PWM2B)

Initialize the analog pin (A0) the potentiometer is connected and the PWM pin (PWM2B) the buzzer is connected.

while true {
    let value = a0.readPercent()
    let frequency = Int(400 + 2000 * value) 
    buzzer.set(frequency: frequency, dutycycle: 0.5)
    sleep(ms: 20) 
}

Since you don't want the control to be available only once, you write the code in the loop while true.

Read the analog value in percentage and store it in the constant value.

Then set the PWM signal. You will need set(frequency:dutycycle:). This method has two parameters: frequency and duty cycle.

Its frequency is related to the analog value above. While the value is too small to be used as a frequency, so you do some calculations.

The duty cycle doesn't really matter in this project, and you could set it to 0.5 here.

Use the function sleep(ms:) to make each pitch will last about 20ms.

Step 7: Run the Project

Download the code to your board. As you rotate the potentiometer, the pitch of the buzzer gradually goes up or go down accordingly.