Software PWM with RPi.GPIO in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is PWM and why is it useful in controlling devices with Raspberry Pi?

PWM stands for Pulse Width Modulation. It lets you control the power delivered to devices like LEDs or motors by switching the power on and off very quickly. This way, you can make an LED dim or a motor run at different speeds without changing the voltage.

beginner

How do you set up a GPIO pin for software PWM using RPi.GPIO?

First, import RPi.GPIO and set the mode (e.g., BCM). Then, set the pin as an output using GPIO.setup(pin, GPIO.OUT). Finally, create a PWM object with GPIO.PWM(pin, frequency) where frequency is in Hertz.

beginner

What does the start() method do in RPi.GPIO PWM?

The start() method begins the PWM signal on the pin with a given duty cycle (percentage of time the signal is ON). For example, start(50) means the signal is ON half the time and OFF half the time.

beginner

How can you change the brightness of an LED using software PWM?

You change the duty cycle of the PWM signal. A higher duty cycle means the LED is ON longer in each cycle, making it brighter. A lower duty cycle means it is ON less, making it dimmer.

beginner

Why should you call stop() and cleanup() when you finish using PWM with RPi.GPIO?

stop() stops the PWM signal on the pin, and cleanup() resets all GPIO pins to their default state. This prevents unwanted signals and frees the pins for other uses.

What does PWM stand for?

A Power Wave Management

B Power Width Modulation

C Pulse Wire Method

D Pulse Width Modulation

PWM means Pulse Width Modulation, a technique to control power by switching on and off quickly.

Which RPi.GPIO method starts the PWM signal on a pin?

A pwm.start()

B GPIO.start()

C GPIO.begin()

D pwm.begin()

The start() method is called on the PWM object to begin the signal.

What does a 75% duty cycle mean for an LED controlled by PWM?

A LED is on 75% of the time

B LED brightness is 25%

C LED blinks 75 times per second

D LED is off 75% of the time

A 75% duty cycle means the LED is ON 75% of the time, making it brighter.

Why do you call GPIO.cleanup() after using PWM?

A To start PWM again

B To reset pins and avoid conflicts

C To increase PWM frequency

D To save power

cleanup() resets GPIO pins to default, preventing conflicts with other programs.

Which frequency unit is used when creating a PWM object in RPi.GPIO?

A Seconds

B Milliseconds

C Hertz

D Volts

Frequency for PWM is given in Hertz (cycles per second).

Explain how to set up and start software PWM on a Raspberry Pi GPIO pin using RPi.GPIO.

Think about the steps from preparing the pin to starting the PWM signal.

Describe how changing the duty cycle affects an LED's brightness when using software PWM.

Relate duty cycle to how long the LED is powered in each cycle.