Servo motor control with PWM in Raspberry Pi

Introduction

Servo motors need special signals to move to the right position. PWM helps send these signals easily.

You want to control the angle of a small robot arm.

You need to open or close a small door automatically.

You want to make a remote-controlled car steer.

You want to move a camera smoothly to look around.

Syntax

Raspberry Pi

import RPi.GPIO as GPIO
import time

pin_number = 12  # Define your pin number here
GPIO.setmode(GPIO.BOARD)
GPIO.setup(pin_number, GPIO.OUT)
pwm = GPIO.PWM(pin_number, 50)  # 50 Hz frequency
pwm.start(7.5)  # Start at middle position

# To change angle:
pwm.ChangeDutyCycle(new_duty_cycle)

# When done:
pwm.stop()
GPIO.cleanup()

Use 50 Hz frequency because servo motors expect a 20 ms period signal.

Duty cycle controls the angle: usually between 2.5% (0°) and 12.5% (180°).

Examples

This example moves the servo to middle, then 0°, then 180° positions.

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)
pwm = GPIO.PWM(12, 50)  # 50 Hz
pwm.start(7.5)  # Middle position

# Move to 0 degrees
pwm.ChangeDutyCycle(2.5)
time.sleep(1)

# Move to 180 degrees
pwm.ChangeDutyCycle(12.5)
time.sleep(1)

pwm.stop()
GPIO.cleanup()

This example sweeps the servo through several angles smoothly.

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BOARD)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 50)
pwm.start(0)

for duty in [2.5, 5, 7.5, 10, 12.5]:
    pwm.ChangeDutyCycle(duty)
    time.sleep(0.5)

pwm.stop()
GPIO.cleanup()

Sample Program

This program moves the servo motor to 0°, 90°, and 180° positions with pauses and prints the current angle. It cleans up GPIO pins at the end.

Raspberry Pi

import RPi.GPIO as GPIO
import time

# Set up GPIO pin 11 for PWM
GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.OUT)

# Create PWM instance at 50 Hz
servo = GPIO.PWM(11, 50)

# Start PWM with 0 duty cycle (servo off)
servo.start(0)

try:
    # Move servo to 0 degrees
    servo.ChangeDutyCycle(2.5)
    print("Servo at 0 degrees")
    time.sleep(1)

    # Move servo to 90 degrees
    servo.ChangeDutyCycle(7.5)
    print("Servo at 90 degrees")
    time.sleep(1)

    # Move servo to 180 degrees
    servo.ChangeDutyCycle(12.5)
    print("Servo at 180 degrees")
    time.sleep(1)

finally:
    # Stop PWM and clean up
    servo.stop()
    GPIO.cleanup()
    print("Cleaned up GPIO")

Important Notes

Always clean up GPIO pins after use to avoid warnings or errors next time.

Servo angles depend on the duty cycle; check your servo's datasheet for exact values.

Use delays after changing duty cycle to give the servo time to move.

Summary

Servo motors use PWM signals to set their angle.

Use 50 Hz frequency and adjust duty cycle between about 2.5% and 12.5% for 0° to 180°.

Always clean up GPIO pins after controlling the servo.