PWM frequency and duty cycle relationship in Raspberry Pi - Mini Project: Build & Apply

PWM Frequency and Duty Cycle Relationship

📖 Scenario: You are working on a Raspberry Pi project that controls the brightness of an LED using PWM (Pulse Width Modulation). You want to understand how changing the PWM frequency and duty cycle affects the LED's brightness.

🎯 Goal: Build a simple Python program that sets up PWM on a GPIO pin, changes the frequency and duty cycle, and prints the current settings to observe their relationship.

📋 What You'll Learn

Create a variable for the GPIO pin number used for PWM

Create a variable for the initial PWM frequency

Create a variable for the initial duty cycle

Use a loop to change the duty cycle from 0 to 100 in steps

Print the current frequency and duty cycle values

💡 Why This Matters

🌍 Real World

PWM is used in many electronics projects to control LED brightness, motor speed, and other devices by adjusting the power delivered.

💼 Career

Understanding PWM is important for embedded systems, robotics, and hardware interfacing roles where precise control of electronic components is required.

1

Set up PWM pin and initial values

Create a variable called pwm_pin and set it to 18. Create a variable called frequency and set it to 1000. Create a variable called duty_cycle and set it to 0.

Raspberry Pi

# Your code here

Need a hint?

Use simple variable assignments for pwm_pin, frequency, and duty_cycle.

2

Import RPi.GPIO and set up PWM

Import the RPi.GPIO module as GPIO. Set the GPIO mode to GPIO.BCM. Set up pwm_pin as an output pin. Create a PWM object called pwm on pwm_pin with the frequency variable frequency. Start PWM with the duty cycle variable duty_cycle.

Raspberry Pi

pwm_pin = 18
frequency = 1000
duty_cycle = 0
# Your code here

Need a hint?

Remember to import the GPIO library and set the pin mode before starting PWM.

3

Change duty cycle in a loop

Use a for loop with variable dc to go from 0 to 100 in steps of 20. Inside the loop, change the PWM duty cycle to dc using pwm.ChangeDutyCycle(dc). Print the current frequency and duty cycle using print(f"Frequency: {frequency} Hz, Duty Cycle: {dc}%").

Raspberry Pi

import RPi.GPIO as GPIO

pwm_pin = 18
frequency = 1000
duty_cycle = 0

GPIO.setmode(GPIO.BCM)
GPIO.setup(pwm_pin, GPIO.OUT)
pwm = GPIO.PWM(pwm_pin, frequency)
pwm.start(duty_cycle)
# Your code here

Need a hint?

Use a for loop with range(0, 101, 20) and update the duty cycle inside the loop.

4

Clean up and stop PWM

After the loop, stop the PWM using pwm.stop(). Clean up the GPIO pins using GPIO.cleanup(). Print "PWM test complete." to show the program finished.

Raspberry Pi

import RPi.GPIO as GPIO
import time

pwm_pin = 18
frequency = 1000
duty_cycle = 0

GPIO.setmode(GPIO.BCM)
GPIO.setup(pwm_pin, GPIO.OUT)
pwm = GPIO.PWM(pwm_pin, frequency)
pwm.start(duty_cycle)

for dc in range(0, 101, 20):
    pwm.ChangeDutyCycle(dc)
    print(f"Frequency: {frequency} Hz, Duty Cycle: {dc}%")
    time.sleep(0.5)
# Your code here

Need a hint?

Remember to stop PWM and clean up GPIO pins to avoid warnings. Then print the completion message.