567 Actuator Assessment and Reference

Learning Objectives

After completing this chapter, you will be able to:

Test your actuator knowledge with interactive quizzes
Use quick reference cards for common specifications
Troubleshoot actuator problems efficiently
Apply actuator selection skills to real-world scenarios

567.1 Interactive Self-Assessment Quiz

Test your understanding of actuators with this auto-graded quiz.

Show code

actuatorQuestions = [
  {
    id: 1,
    question: "You need to control a robot arm that requires precise positioning at specific angles (0, 45, 90, 135 degrees). Which actuator is most appropriate?",
    choices: [
      "DC motor with PWM speed control",
      "Servo motor with angle control",
      "Stepper motor with step counting",
      "Relay for on/off control"
    ],
    correct: 1,
    explanation: "Servo motors are designed for precise angular positioning, typically 0-180 degrees. They have built-in feedback control that maintains the commanded angle."
  },
  {
    id: 2,
    question: "Your microcontroller GPIO pin can safely source 20mA at 3.3V. You need to control a 12V DC motor that draws 500mA. What is the correct approach?",
    choices: [
      "Connect the motor directly to the GPIO pin",
      "Use a transistor or MOSFET with a separate 12V power supply",
      "Reduce motor voltage to 3.3V to match the GPIO",
      "Use multiple GPIO pins in parallel"
    ],
    correct: 1,
    explanation: "GPIO pins cannot drive high-current loads directly. Use a transistor (2N2222, BC547) or MOSFET as a switch with a separate 12V power supply and flyback diode."
  },
  {
    id: 3,
    question: "A 3D printer uses NEMA 17 stepper motors for precise positioning. What advantage do stepper motors provide over servo motors for this application?",
    choices: [
      "Stepper motors are cheaper than servo motors",
      "Stepper motors provide open-loop position control without feedback sensors",
      "Stepper motors run faster than servo motors",
      "Stepper motors consume less power"
    ],
    correct: 1,
    explanation: "Stepper motors provide precise position control by counting steps without requiring encoders (open-loop). This simplifies design and reduces cost for applications like 3D printers."
  },
  {
    id: 4,
    question: "You're controlling LED brightness using PWM at 1kHz with 8-bit resolution (0-255). What duty cycle percentage corresponds to a PWM value of 64?",
    choices: [
      "64%",
      "25%",
      "32%",
      "50%"
    ],
    correct: 1,
    explanation: "PWM duty cycle = (PWM_value / Max_value) x 100 = (64 / 255) x 100 = 25.1% approximately 25%."
  },
  {
    id: 5,
    question: "Your ESP32 project controls a relay that switches a 120V AC heater. Why is a flyback diode necessary across the relay coil?",
    choices: [
      "To prevent AC voltage from backfeeding into the ESP32",
      "To suppress inductive voltage spike when relay coil is de-energized",
      "To reduce power consumption of the relay",
      "To speed up relay switching time"
    ],
    correct: 1,
    explanation: "Relay coils are inductors. When power is cut, the collapsing magnetic field generates a high voltage spike that can destroy transistors or microcontrollers. A flyback diode provides a safe path for this current."
  }
]

viewof currentQ = Inputs.range([0, actuatorQuestions.length - 1], {
  step: 1,
  value: 0,
  label: "Question Number"
})

md`### Question ${currentQ + 1} of ${actuatorQuestions.length}

${actuatorQuestions[currentQ].question}`

Show code

viewof userAnswer = Inputs.radio(
  actuatorQuestions[currentQ].choices,
  {label: "Your Answer:"}
)

viewof showAnswer = Inputs.toggle({label: "Show Answer", value: false})

feedback = {
  if (showAnswer) {
    const correctIdx = actuatorQuestions[currentQ].correct;
    const correctAnswer = actuatorQuestions[currentQ].choices[correctIdx];
    const isCorrect = userAnswer === correctAnswer;

    return html`<div style="padding: 15px; margin: 10px 0; border-radius: 5px; background-color: ${isCorrect ? '#d4edda' : '#f8d7da'};">
      <strong style="color: ${isCorrect ? '#155724' : '#721c24'};">
        ${isCorrect ? 'Correct!' : 'Incorrect'}
      </strong>
      <p><strong>Correct answer:</strong> ${correctAnswer}</p>
      <p><strong>Explanation:</strong> ${actuatorQuestions[currentQ].explanation}</p>
    </div>`;
  }
  return html`<p style="color: #666;">Toggle "Show Answer" to see feedback.</p>`;
}

567.2 Quick Reference Cards

Reference Card 1: Common Actuator Specifications

Actuator	Voltage	Current	Control Interface	Key Specs
Servo SG90	4.8-6V	500mA stall	PWM (1000-2000us)	180 deg range
Servo MG996R	4.8-7.2V	2.5A stall	PWM (1000-2000us)	Metal gears
DC Motor (TT)	3-6V	200-500mA	PWM + H-Bridge	200-300 RPM
Stepper 28BYJ-48	5V	200mA	4-wire sequential	2048 steps/rev
Stepper NEMA 17	12V	1.2A	A4988/DRV8825	200 steps/rev
Relay 5V	5V coil	70mA coil	Digital ON/OFF	10A @ 250VAC
Solenoid 12V	12V	500mA-1A	Digital ON/OFF	10mm stroke
NeoPixel WS2812B	5V	60mA/pixel max	Digital data	Addressable RGB
Buzzer (Passive)	3-5V	20mA	PWM tone	Variable frequency

Reference Card 2: Motor Driver Pinouts

567.2.1 L298N H-Bridge Motor Driver

Pins	Function
IN1, IN2	Motor A direction
IN3, IN4	Motor B direction
ENA, ENB	PWM speed (remove jumper)
OUT1, OUT2	Motor A connections
OUT3, OUT4	Motor B connections
+12V	Motor supply (5-35V)
+5V	Logic output (when >7V input)
GND	Common ground

Truth Table:

ENA	IN1	IN2	Motor State
0	X	X	STOP (coast)
1	0	0	BRAKE
1	1	0	FORWARD
1	0	1	REVERSE
1	1	1	BRAKE

567.2.2 A4988 Stepper Driver

Pin	Function
STEP	Pulse for each step
DIR	Direction (H/L)
ENABLE	LOW=on, HIGH=off
MS1, MS2, MS3	Microstepping
1A, 1B, 2A, 2B	Motor coils
VMOT	8-35V motor supply
VDD	3-5.5V logic

Reference Card 3: PWM Control Formulas

ESP32 PWM Setup:

const int pwmFreq = 5000;      // Frequency in Hz
const int pwmChannel = 0;       // 0-15 available
const int pwmResolution = 8;    // 8-bit = 0-255

ledcSetup(pwmChannel, pwmFreq, pwmResolution);
ledcAttachPin(GPIO_PIN, pwmChannel);
ledcWrite(pwmChannel, dutyCycle);

Formulas:

Duty Cycle (%) = (PWM value / Max value) x 100
Average Voltage = Supply Voltage x Duty Cycle

8-bit PWM:  Max = 255
10-bit PWM: Max = 1023
12-bit PWM: Max = 4095

Servo Timing (50 Hz):

1000 microseconds = 0 degrees
1500 microseconds = 90 degrees
2000 microseconds = 180 degrees

Reference Card 4: Actuator Troubleshooting

Problem	Likely Cause	Solution
Motor doesn’t run	Wrong wiring	Check IN1, IN2, EN connections
Motor only one direction	Direction pins swapped	Swap IN1 and IN2
Motor runs but slow	Low PWM duty cycle	Increase duty cycle
Servo jitters	Insufficient power	Use external 5V supply
Servo doesn’t move	Wrong frequency	Must be 50Hz for servos
Stepper skips steps	Too fast	Reduce speed, add acceleration
Driver overheats	Current too high	Add heatsink, reduce current
Random MCU resets	Missing flyback diode	Add diode across inductive loads
Relay won’t switch	Coil voltage wrong	Check coil voltage rating
LED very dim	Missing current limit	Add 220-330 ohm resistor

567.3 Chapter Summary

Actuators are the hands of IoT systems, converting electrical signals from microcontrollers into physical actions that affect the real world.

567.3.1 Key Takeaways

Motor Types: DC (continuous rotation), Servo (precise angles), Stepper (precise steps)
Driver Circuits: Required for high-current loads (L298N, A4988, transistors)
PWM Control: Enables smooth speed/brightness control by varying duty cycle
Safety: Flyback diodes, current limiting, watchdog timers, fail-safe defaults
Visual/Audio: LEDs, displays, buzzers provide user feedback

567.3.2 Motor Selection Quick Guide

Need	Choose	Why
Variable speed, no position	DC Motor	Simple, efficient, cheap
Precise angle (0-180 deg)	Servo	Built-in feedback, easy control
Precise position, any range	Stepper	Open-loop accuracy, holds position
On/off, high power	Relay	Electrical isolation, high current
Fast linear motion	Solenoid	Quick push/pull action

567.4 What’s Next?

Now that you understand actuators (output devices), you can combine them with sensors (input devices) to create complete IoT feedback control systems.

Return to Actuators Overview →

Continue to Mobile Phone as a Sensor →