Servo motor control with PWM in Raspberry Pi - Mini Project: Build & Apply

Servo motor control with PWM

📖 Scenario: You have a small servo motor connected to your Raspberry Pi. You want to control its position by sending the right pulse width modulation (PWM) signals.Servo motors move to a position based on the length of the pulse they receive. By changing the pulse width, you can make the servo point to different angles.

🎯 Goal: Build a simple Python program that sets up PWM on a GPIO pin and moves the servo motor to a specific angle.

📋 What You'll Learn

Use the RPi.GPIO library to control GPIO pins

Set up PWM on GPIO pin 18

Calculate the correct duty cycle for a given servo angle

Move the servo to 90 degrees

Print the duty cycle used

💡 Why This Matters

🌍 Real World

Servo motors are used in robotics, remote-controlled vehicles, and home automation to control precise movements like steering or opening doors.

💼 Career

Understanding PWM control of servos is important for embedded systems engineers, robotics developers, and IoT device programmers.

1

Set up GPIO and PWM

Import the RPi.GPIO library as GPIO. Set the GPIO mode to GPIO.BCM. Create a PWM instance called pwm on GPIO pin 18 with frequency 50 Hz.

Raspberry Pi

import RPi.GPIO as GPIO
# Set GPIO mode and create PWM instance on pin 18 at 50Hz
# Your code here

Need a hint?

Use GPIO.setmode(GPIO.BCM) to select pin numbering. Then set pin 18 as output. Finally, create PWM on pin 18 with 50Hz frequency.

2

Start PWM with 0 duty cycle

Start the pwm instance with a duty cycle of 0 to initialize the servo control.

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 50)
# Start PWM with 0 duty cycle
# Your code here

Need a hint?

Use pwm.start(0) to begin PWM with zero duty cycle.

3

Calculate duty cycle for 90 degrees

Create a variable called angle and set it to 90. Calculate the duty cycle for this angle using the formula duty = (angle / 18) + 2. Store the result in a variable called duty.

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 50)
pwm.start(0)
# Set angle to 90 and calculate duty cycle
# Your code here

Need a hint?

The duty cycle for a servo angle is usually calculated as (angle / 18) + 2.

4

Move servo and print duty cycle

Use pwm.ChangeDutyCycle(duty) to move the servo to the calculated position. Then print the duty cycle value using print(f"Duty cycle set to: {duty}"). Finally, clean up GPIO with GPIO.cleanup().

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 50)
pwm.start(0)
angle = 90
duty = (angle / 18) + 2
# Move servo and print duty cycle
# Your code here

Need a hint?

Use pwm.ChangeDutyCycle(duty) to move the servo. Then print the duty cycle with an f-string. Don't forget to clean up GPIO.