ESP32 PWM
(Pulse Width Modulation) 🔗

Introduction to PWM

PWM (Pulse Width Modulation):

  • A technique to produce analog-like signals using digital means.
  • Varies the width of pulses in a sequence to represent a range of analog values.

Applications:

  • Motor speed control
  • LED brightness control
  • Signal generation, and more!

A 5Hz square wave:

A 10Hz square wave:

A PWM wave:

A PWM wave:

Function Explanations for PWM

from machine import Pin, PWM

pwm = PWM(Pin(5), freq=1000, duty=512)

pwm.freq(100)
pwm.duty(512)
  • Pin(NUMBER): Define a pin.
  • PWM(pin, freq=1000, duty=512): Create a PWM object for the specified pin.
  • pwm.duty(VALUE): Set the duty cycle. (0 - 1023)
  • pwm.freq(VALUE): Set the frequency. (HZ)

Wokwi Logic Analyzer

Wokwi Logic Analyzer

PulseView -- HomePage

PulseView -- Download

PulseView

PulseView

PulseView

PulseView

PulseView

PulseView

PulseView

PulseView

Hardware Connections - LED

LED:

  • Anode connected to Pin 5.
  • Cathode to GND via 220Ω resistor.

PWM - LED 🔗

Dynamic LED Brightness Control

Changing LED Brightness Over Time:

led_pin = Pin(5)
led_pwm = PWM(led_pin)
# Increasing brightness
for duty in range(0, 1024, 64):
    led_pwm.duty(duty)
    time.sleep(0.5)
# Decreasing brightness
for duty in range(1023, -1, -64):
    led_pwm.duty(duty)
    time.sleep(0.5)

Hardware Connections - Motor

Motor 規格:

  • 重量：9g

  • 尺寸：23*12.2*29mm

  • 工作電壓：4.8V

  • 轉矩：1.8kg-cm，當工作電壓為4.8V時

  • 運轉速度：0.1秒 ∕ 60度 ，當工作電壓為4.8V時

  • 脈衝寬度範圍：500~2400µs

  • 死頻帶寬度（dead band width）：10µs

Hardware Connections - Motor

Motor 規格:

  • 伺服馬達有三條線:

    • 電源 (Power)
    • 接地 (Ground)
    • 訊號線 (Signal)

  • 訊號線用於傳送PWM脈波來控旋轉角度。

  • PWM脈波的頻率是50Hz。

  • 脈衝的持續時間:

    • 0.5ms 代表 0 度
    • 2.4ms 代表 180 度

Dynamic Motor Speed Control 

# PWM frequency for the servo
pwm_freq = 50

# The width (duration) of each pulse for the given frequency
pwm_width = 1 / pwm_freq

# Define the range of angles the servo can rotate to
min_angle, max_angle = 0, 180

# Define the pulse widths (in seconds) corresponding to the minimum and maximum angles for the servo
min_width, max_width = float('500e-06'), float('2400e-06')

# Calculate the duty cycle values for the minimum and maximum pulse widths
min_duty = min_width / pwm_width
max_duty = max_width / pwm_width

# Determine the conversion factor to map an angle to its corresponding duty cycle
angle_conversion_factor = (max_duty - min_duty) / (max_angle - min_angle)

Dynamic Motor Speed Control 

def rotate(servo, degree, delay=0.4):
    """
    Rotate the servo to the desired angle.
    
    Parameters:
    - servo: The servo object.
    - degree: The desired angle to rotate the servo to (0 to 180 degrees).
    - delay: Time (in seconds) to wait after rotating the servo. Default is 0.4 seconds.
    """
    
    # Calculate the duty cycle for the desired angle
    dc = angle_conversion_factor * degree + min_duty
    
    # Uncomment the next line if using MicroPython with the `duty_u16` method
    #servo.duty_u16(int(65535 * dc))
    
    #Set the servo's duty cycle to move it to the desired angle
    servo.duty(int(1023 * dc))
    
    # Wait for the specified delay to let the servo move and settle
    sleep(delay)

Dynamic Motor Speed Control 

Hardware Connections - Speaker

Speaker:

  • Positive Pin to Pin 5.
  • Negative Pin to GND.

Hardware Connections - Speaker

Speaker Ambulance Ring

Playing Tones with a Speaker

Frequency & Pitch: The frequency set determines the pitch of the sound produced. Higher frequencies result in higher pitched sounds.

Duty & Volume: The duty cycle impacts the volume of the sound. A 50% duty cycle (512 out of 1024) typically produces clear sound without distortion.

Solfège is a method used to teach pitch and sight singing. In this system, each note is given a name, making it easier to remember and sing.

Solfège Standard Note Name Frequency (Hz)
Do C 262
Re D 294
Mi E 330
Fa F 349
Sol G 392
La A 440
Si B 494
Do C 523

Playing Tones with a Speaker

Playing Tones with a Speaker

from machine import Pin, PWM
import time

# Dictionary to map standard note names to frequencies
standard_to_freq = {
    'C': 262,
    'D': 294,
    'E': 330,
    'F': 349,
    'G': 392,
    'A': 440,
    'B': 494,
    'C_high': 523
}

# Define the speaker pin and PWM object
speaker_pin = Pin(7)
speaker_pwm = PWM(speaker_pin)

# Let's play "Twinkle Twinkle Little Star" using standard note names
song = ['C', 'C', 'G', 'G', 'A', 'A', 'G', 'F', 'F', 'E', 'E', 'D', 'D', 'C']
for note in song:
    frequency = standard_to_freq[note]
    speaker_pwm.freq(frequency)
    speaker_pwm.duty(512)
    time.sleep(0.5)
    speaker_pwm.duty(0)  # Turning off between notes
    time.sleep(0.1)

Playing Tones with a Speaker

from machine import Pin, PWM
import time

# Dictionary to map standard note names to frequencies
standard_to_freq = {
    'C': 262,
    'D': 294,
    'E': 330,
    'F': 349,
    'G': 392,
    'A': 440,
    'B': 494,
    'C_high': 523
}

# Define the speaker pin and PWM object
speaker_pin = Pin(5)
speaker_pwm = PWM(speaker_pin)

# Let's play "Twinkle Twinkle Little Star" using standard note names
song = ['C', 'C', 'G', 'G', 'A', 'A', 'G', 'F', 'F', 'E', 'E', 'D', 'D', 'C']
for note in song:
    frequency = standard_to_freq[note]
    speaker_pwm.freq(frequency)
    speaker_pwm.duty(512)
    time.sleep(0.5)
    speaker_pwm.duty(0)  # Turning off between notes
    time.sleep(0.1)

Playing Tones with a Speaker

Conclusion

PWM offers versatile control over devices like LEDs, motors, and speakers. By understanding frequency and duty cycle, you can fine-tune device behaviors, ranging from LED brightness to musical notes and motor speed.