Duty cycle control for motor/LED in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a duty cycle in the context of controlling a motor or LED?

Duty cycle is the percentage of time a signal is ON compared to the total time of one cycle. It controls how much power the motor or LED receives.

beginner

How does changing the duty cycle affect an LED's brightness?

Increasing the duty cycle makes the LED brighter because it is ON for a longer time in each cycle. Decreasing it makes the LED dimmer.

intermediate

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

PWM (Pulse Width Modulation) is a technique that switches power ON and OFF rapidly. It controls power by adjusting the duty cycle, allowing smooth speed or brightness control.

intermediate

In embedded C, which hardware feature is commonly used to generate PWM signals?

Timers or timer modules in microcontrollers are used to generate PWM signals by toggling output pins at set intervals.

intermediate

Why is it better to use PWM for motor speed control instead of just changing voltage?

PWM efficiently controls motor speed without wasting power as heat, unlike changing voltage which can cause energy loss and unstable motor behavior.

What does a 50% duty cycle mean for an LED?

A LED is ON half the time and OFF half the time

B LED is always ON

C LED is always OFF

D LED blinks twice as fast

A 50% duty cycle means the LED is ON for half the cycle and OFF for the other half.

Which embedded C feature is typically used to create PWM signals?

A Timers

B Interrupts

C Serial communication

D ADC (Analog to Digital Converter)

Timers generate PWM by switching output pins ON and OFF at precise intervals.

What happens to motor speed if you increase the PWM duty cycle?

A Motor speed decreases

B Motor speed increases

C Motor stops

D Motor speed stays the same

Increasing duty cycle means more power to the motor, so it spins faster.

Why is PWM preferred over varying voltage for LED brightness control?

A Varying voltage is faster

B Varying voltage is easier and better

C PWM is more energy efficient and provides smooth control

D PWM damages LEDs

PWM saves energy and allows precise brightness control without damaging the LED.

If a PWM signal has a period of 10 ms and the ON time is 2 ms, what is the duty cycle?

A 50%

B 2%

C 80%

D 20%

Duty cycle = (ON time / Period) * 100 = (2 ms / 10 ms) * 100 = 20%

Explain how PWM controls the brightness of an LED or the speed of a motor using duty cycle.

Think about how turning power ON and OFF quickly changes the average power.

Describe how you would implement duty cycle control for a motor in embedded C using a timer.

Consider how timers toggle output pins and how changing ON time affects the motor.