LED brightness control in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is PWM and why is it used for LED brightness control?

PWM stands for Pulse Width Modulation. It controls LED brightness by switching the LED on and off very fast. The longer the LED is on compared to off, the brighter it looks.

beginner

How do you set up a GPIO pin on Raspberry Pi for PWM to control an LED?

You first import the GPIO library, set the pin mode to BCM or BOARD, then set the pin as output. After that, you create a PWM instance on that pin with a frequency, and start it with a duty cycle.

beginner

What does the duty cycle in PWM represent?

The duty cycle is the percentage of time the signal is ON during one cycle. For example, 50% means the LED is on half the time and off half the time, making it appear half as bright.

intermediate

Why can't we just use a resistor to change LED brightness instead of PWM?

Using a resistor changes current but wastes power as heat and is less efficient. PWM controls brightness by switching on/off quickly, saving power and allowing smooth brightness control.

beginner

What Python library is commonly used on Raspberry Pi to control GPIO pins for LED brightness?

The RPi.GPIO library is commonly used. It allows you to set up pins, create PWM signals, and control LED brightness easily.

What does PWM stand for in LED brightness control?

A Pulse Width Modulation

B Power Wave Management

C Pulse Wave Measurement

D Power Width Modulation

PWM means Pulse Width Modulation, which controls brightness by changing how long the LED is on in each cycle.

In PWM, what happens if the duty cycle is 100%?

A LED is fully on

B LED is off

C LED blinks slowly

D LED is half bright

A 100% duty cycle means the LED is on all the time, so it is fully bright.

Which Raspberry Pi pin mode can be used to refer to pins by their physical location?

A BCM

B BOARD

C PWM

D GPIO

BOARD mode refers to pins by their physical position on the Raspberry Pi header.

Why is PWM preferred over using a resistor to control LED brightness?

A PWM wastes more power

B Resistor is more efficient

C PWM allows smooth brightness control and saves power

D Resistor changes color

PWM saves power and allows smooth brightness changes by switching the LED on and off quickly.

Which Python command starts PWM on a GPIO pin with a duty cycle of 75%?

A GPIO.output(75)

B GPIO.setup(75)

C pwm.start(75)

D pwm.ChangeDutyCycle(75)

The pwm.start(75) command starts PWM with a 75% duty cycle, making the LED 75% bright.

Explain how PWM controls LED brightness on a Raspberry Pi.

Think about how turning the LED on and off quickly changes how bright it looks.

Describe the steps to set up PWM on a Raspberry Pi GPIO pin to control an LED.

Remember the order of commands to prepare the pin and start PWM.