PWMLED for brightness in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output brightness level?

Consider this Python code using gpiozero's PWMLED to set brightness. What brightness value will be printed?

Raspberry Pi

from gpiozero import PWMLED
led = PWMLED(17)
led.value = 0.5
print(led.value)

A 0.0

B None

C 1.0

D 0.5

💡 Hint

The value property sets brightness from 0 (off) to 1 (full brightness).

The PWMLED.value property holds the brightness level as a float between 0 and 1. Setting it to 0.5 means half brightness, so printing led.value outputs 0.5.

❓ Predict Output

intermediate

What happens if you set PWMLED value to 1.5?

What will happen when running this code snippet?

Raspberry Pi

from gpiozero import PWMLED
led = PWMLED(17)
led.value = 1.5
print(led.value)

A ValueError is raised

B led.value prints 0.0

C led.value prints 1.5

D led.value prints 1.0

💡 Hint

PWMLED.value must be between 0 and 1 inclusive.

Setting led.value to 1.5 is invalid because brightness must be between 0 and 1. This raises a ValueError.

🔧 Debug

advanced

Why does this PWMLED code not change brightness?

This code tries to set brightness but the LED stays off. What is the problem?

Raspberry Pi

from gpiozero import PWMLED
led = PWMLED(17)
led.value = -0.1
print(led.value)

A PWMLED does not support setting value directly

B LED pin 17 is wrong, so no brightness change

C Negative brightness is invalid and ignored, so LED stays off (value 0)

D The print statement causes the LED to turn off

💡 Hint

Brightness values must be between 0 and 1 inclusive.

Setting led.value to a negative number is invalid. The PWMLED class clamps the value to 0, so the LED stays off.

🧠 Conceptual

advanced

How does PWMLED control brightness?

Which best describes how PWMLED changes LED brightness?

A It turns the LED on and off very fast to simulate brightness levels

B It changes the voltage supplied to the LED continuously

C It changes the LED color to appear dimmer

D It uses a resistor to reduce current for brightness control

💡 Hint

PWM means Pulse Width Modulation.

PWMLED uses Pulse Width Modulation: it switches the LED on and off very quickly. The ratio of on-time to off-time controls perceived brightness.

❓ Predict Output

expert

What is the final brightness value after this sequence?

What value will be printed after running this code?

Raspberry Pi

from gpiozero import PWMLED
led = PWMLED(17)
led.value = 0.3
led.value += 0.4
led.value -= 0.1
print(round(led.value, 2))

A 0.0

B 0.6

C 0.7

D 0.5

💡 Hint

Remember PWMLED.value clamps between 0 and 1.

Starting at 0.3, adding 0.4 gives 0.7, subtracting 0.1 gives 0.6. The final value is 0.6.