Actuators & Control · Study deck
PWM Control: Signals and Duty-Cycle Behaviour
PWM switches power on and off in short pulses.
Motor Max is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Explain: PWM Resolution: The number of discrete duty cycle steps; ESP32 LEDC peripheral: 1-16 bit configurable; Arduino Uno: 8-bit (256 steps); higher resolution provides finer control but requires more timer bits.
- Explain: The right setting is not just a number from 0 to 255; it is a duty, frequency, ramp, and feedback choice that keeps motion, brightness, heat, or position under control.
- Explain: PWM is the controller's way to ask for less or more effort, but the physical result depends on frequency, duty cycle, driver losses, motor inertia, and the load.
Major section
Start With the Story
A changing command number is not enough; the reviewer needs the drive timing, supply condition, and measured fan result.
- An actuator is a device that turns an electrical command into physical action.
- A microcontroller is a small computer built to read inputs and control outputs.
- Modulation means changing a signal over time to carry a setting.
Major section
Start With the Story (continued)
This runway does not prove motor life or make one switching rate safe for every load.
- The deeper sections cover waveform timing, driver stages, resolution, filtering, load limits, and measurement.
- PWM is the controller's way to ask for less or more effort, but the physical result depends on frequency, duty cycle, driver losses, motor inertia, and the load.
- The right setting is not just a number from 0 to 255; it is a duty, frequency, ramp, and feedback choice that keeps motion, brightness, heat, or position under control.
Major section
In 60 Seconds
It enables precise control of motor speed, LED brightness, and servo position using simple digital microcontroller pins without analog hardware.
- Pulse Width Modulation (PWM) is a digital technique that simulates analog control by rapidly switching power on and off at a specific duty cycle.
Major section
Key Concepts
Duty Cycle: The percentage of one PWM period during which the signal is HIGH; 0% = always off, 100% = always on; controls LED brightness, motor speed, heater temperature, and servo position (within a specific pulse width range).
- PWM Resolution: The number of discrete duty cycle steps; ESP32 LEDC peripheral: 1-16 bit configurable; Arduino Uno: 8-bit (256 steps); higher resolution provides finer control but requires more timer bits.
Major section
How It Works: PWM Creates "Fake" Analog Voltage
You can't push continuously (analog), but you can push in pulses (digital).
- Example: 50% duty cycle = ON for 0.5 ms, OFF for 0.5 ms, repeat at 1kHz = motor sees ~2.5V average from a 5V supply.
Major section
Putting Numbers to It
At 5kHz PWM with 50% duty cycle, each period is T=1/5000=200 μs.
- The signal is HIGH for ton=0.5×200=100 μs and LOW for 100 μs.
Major section
Try It: PWM Motor Speed Control
Reverse the H-bridge only after the shaft response is understood, and finally sweep frequency to distinguish audible whine from excessive switching loss.
- The useful result is a bounded operating region, not one attractive speed reading.
Major section
Why Duty Cycle Matters for IoT
Energy Efficiency: LED at 50% duty cycle uses approximately 50% power, extending battery life.
- No Analog Hardware: Digital MCUs can control analog-like behavior without DAC chips.
- Key insight: The actuator "sees" the average voltage, smoothed by its physical response time.
Major section
Worked Example: Smart Greenhouse Ventilation Fan
A greenhouse uses a 12V DC fan (rated 0.5A at full speed) controlled by an ESP32 via a MOSFET driver.
- Choosing 20 kHz pushes the hum above hearing range, making the fan appear to run silently at any speed.
Deck summary
Key takeaways
A changing command number is not enough; the reviewer needs the drive timing, supply condition, and measured fan result.
- This runway does not prove motor life or make one switching rate safe for every load.
- It enables precise control of motor speed, LED brightness, and servo position using simple digital microcontroller pins without analog hardware.
- Duty Cycle: The percentage of one PWM period during which the signal is HIGH; 0% = always off, 100% = always on; controls LED brightness, motor speed, heater temperature, and servo position (within a specific pulse width range).
- You can't push continuously (analog), but you can push in pulses (digital).
Retrieval practice
Recall check 1 of 4
Motor Max says: answer from memory, then check your reasoning.
Q1An ideal motor drive applies 12V across the motor during each PWM on interval and 0V during each off interval, at 75% duty and 5kHz. What is the time-average terminal voltage?
Show answer
Answer: A For the stated ideal terminal waveform, 75% at 12V and 25% at 0V gives a time-average voltage of 9V.
Retrieval practice
Recall check 2 of 4
Motor Max says: answer from memory, then check your reasoning.
Q2A fan hums at its PWM rate. What trade-off should guide a frequency change?
Show answer
Answer: A Higher rates may quiet hum while increasing switch loss.
Retrieval practice
Recall check 3 of 4
Motor Max says: answer from memory, then check your reasoning.
Q3An ESP32 drives a motor and an LED with different PWM needs. What setup is sound?
Show answer
Answer: A The PWM setup must fit each load before its command is sent.
Retrieval practice
Recall check 4 of 4
Motor Max says: answer from memory, then check your reasoning.
Q4A hobby servo holds the wrong angle although its frame rate is accepted. Which setting most directly changes the target angle?
Show answer
Answer: D The servo interprets the width of its control pulse as the position command.
Print reference
Answers
Answer key.
- A · For the stated ideal terminal waveform, 75% at 12V and 25% at 0V gives a time-average voltage of 9V.
- A · Higher rates may quiet hum while increasing switch loss.
- A · The PWM setup must fit each load before its command is sent.
- D · The servo interprets the width of its control pulse as the position command.