Servo Motor Control for Arduino Uno

Generate complete servo motor control code for Arduino Uno using the standard Arduino Servo library.

Quick Start

When user requests servo control, generate code that:

•Uses standard Servo.h library (built-in)
•Selects appropriate PWM-capable pin
•Handles Timer1 usage properly
•Implements requested behavior (sweep, position, interactive)

Platform Requirements

Refer to arduino-uno platform skill for:

•Complete ATmega328P pin specifications
•PWM capabilities and timer assignments
•Memory constraints (2KB SRAM, 32KB Flash)
•Communication interfaces (UART, I2C, SPI)
•Current limitations and power requirements

Key constraints for servo (from Arduino Uno platform):

•✅ PWM pins: 3, 5, 6, 9, 10, 11
•⚠️ Servo library uses Timer1, which disables PWM on pins 9 and 10
•⚠️ Operating voltage: 5V logic
•⚠️ Max current per pin: 40 mA (recommended 20 mA)
•⚠️ Limited RAM: Only 2KB SRAM (be memory-conscious)

Arduino Framework Basics

Program Structure

cpp

void setup() {
  // Runs once at startup
  // Initialize pins, Serial, peripherals
}

void loop() {
  // Runs continuously after setup()
  // Main program logic
}

Serial Communication

cpp

Serial.begin(9600);           // Initialize Serial (standard baud rate)
Serial.println("Hello");      // Print with newline
Serial.print(value);          // Print without newline
if (Serial.available()) {     // Check if data available
  char c = Serial.read();     // Read one byte
}

Timing Functions

cpp

delay(1000);                  // Delay 1000ms (blocking)
delayMicroseconds(100);       // Delay 100μs (blocking)
unsigned long ms = millis();  // Milliseconds since boot (rolls over ~49 days)
unsigned long us = micros();  // Microseconds since boot (rolls over ~70 minutes)

Math and Mapping

cpp

int mapped = map(value, 0, 1023, 0, 255);  // Map range
int limited = constrain(value, 0, 255);    // Constrain to range

Arduino Uno-Specific: Timer1 for Servo

Critical understanding: The Servo library uses Timer1 for precise pulse timing.

Timer1 Impact

•PWM on pins 9 and 10 is DISABLED when servo is attached
•Cannot use analogWrite(9, ...) or analogWrite(10, ...)
•Timer1 no longer available for other timing functions
•This affects ALL servos, even if attached to other pins

Why This Matters

Arduino Uno has three timers:

•Timer0: Used by millis(), delay(), PWM on pins 5 and 6
•Timer1: Used by Servo library, PWM on pins 9 and 10
•Timer2: Used by tone(), PWM on pins 3 and 11

Once you use the Servo library, Timer1 is dedicated to servo control.

Pin Selection

PWM-Capable Pins for Servo

Arduino Uno PWM pins: 3, 5, 6, 9, 10, 11

Recommended Servo Pins

Best choices: 9, 10 (490Hz PWM, better for servos) Acceptable: 3, 11 (490Hz) Avoid: 5, 6 (980Hz PWM, can cause servo jitter)

Default Pin

If user doesn't specify: Use Pin 9

⚠️ Remember: PWM on pins 9 and 10 will be disabled once Servo library is used!

Code Generation

Basic Servo Sweep Example

cpp

#include <Servo.h>

Servo myServo;

const int servoPin = 9;  // PWM-capable pin

void setup() {
  Serial.begin(9600);

  myServo.attach(servoPin);  // Attach servo to pin

  // Move to center position
  myServo.write(90);
  delay(500);

  Serial.println("Servo initialized");
}

void loop() {
  // Sweep from 0 to 180 degrees
  Serial.println("Sweeping 0 -> 180");
  for (int pos = 0; pos <= 180; pos++) {
    myServo.write(pos);
    delay(15);  // 15ms delay for smooth movement
  }

  delay(500);

  // Sweep from 180 to 0 degrees
  Serial.println("Sweeping 180 -> 0");
  for (int pos = 180; pos >= 0; pos--) {
    myServo.write(pos);
    delay(15);
  }

  delay(500);
}

Fixed Position Example

cpp

#include <Servo.h>

Servo myServo;
const int servoPin = 9;

void setup() {
  Serial.begin(9600);

  myServo.attach(servoPin);

  // Set to specific position (0-180 degrees)
  myServo.write(90);  // Center position

  Serial.println("Servo at 90 degrees");
}

void loop() {
  // Servo holds position
  // No need to continuously write
}

Interactive Control (Serial Input)

cpp

#include <Servo.h>

Servo myServo;
const int servoPin = 9;

void setup() {
  Serial.begin(9600);

  myServo.attach(servoPin);
  myServo.write(90);

  Serial.println("Servo Control Ready");
  Serial.println("Enter angle (0-180):");
}

void loop() {
  if (Serial.available() > 0) {
    int angle = Serial.parseInt();

    // Validate range
    if (angle >= 0 && angle <= 180) {
      myServo.write(angle);
      Serial.print("Servo moved to: ");
      Serial.println(angle);
    } else {
      Serial.println("Invalid angle. Enter 0-180.");
    }

    // Clear remaining input
    while (Serial.available() > 0) {
      Serial.read();
    }
  }
}

Potentiometer Control

cpp

#include <Servo.h>

Servo myServo;

const int servoPin = 9;
const int potPin = A0;

void setup() {
  Serial.begin(9600);
  myServo.attach(servoPin);
}

void loop() {
  // Read potentiometer (0-1023)
  int potValue = analogRead(potPin);

  // Map to servo angle (0-180)
  int angle = map(potValue, 0, 1023, 0, 180);

  // Move servo
  myServo.write(angle);

  // Optional: print current position
  Serial.print("Pot: ");
  Serial.print(potValue);
  Serial.print(" -> Angle: ");
  Serial.println(angle);

  delay(15);  // Small delay for stability
}

Button Control (Increment Position)

cpp

#include <Servo.h>

Servo myServo;

const int servoPin = 9;
const int buttonPin = 2;

int currentAngle = 90;
int lastButtonState = HIGH;
unsigned long lastDebounceTime = 0;
const unsigned long debounceDelay = 50;

void setup() {
  Serial.begin(9600);

  pinMode(buttonPin, INPUT_PULLUP);
  myServo.attach(servoPin);
  myServo.write(currentAngle);

  Serial.println("Press button to increment servo position");
}

void loop() {
  int reading = digitalRead(buttonPin);

  // Debounce button
  if (reading != lastButtonState) {
    lastDebounceTime = millis();
  }

  if ((millis() - lastDebounceTime) > debounceDelay) {
    if (reading == LOW && lastButtonState == HIGH) {
      // Button pressed
      currentAngle += 15;
      if (currentAngle > 180) {
        currentAngle = 0;  // Wrap around
      }

      myServo.write(currentAngle);
      Serial.print("Angle: ");
      Serial.println(currentAngle);
    }
  }

  lastButtonState = reading;
}

Multiple Servos (Limited by Timer)

cpp

#include <Servo.h>

Servo servo1;
Servo servo2;

const int servo1Pin = 9;
const int servo2Pin = 10;

void setup() {
  Serial.begin(9600);

  servo1.attach(servo1Pin);
  servo2.attach(servo2Pin);

  // Different positions
  servo1.write(45);
  servo2.write(135);

  Serial.println("Multiple servos initialized");
}

void loop() {
  // Synchronized movement
  for (int pos = 0; pos <= 180; pos++) {
    servo1.write(pos);
    servo2.write(180 - pos);  // Mirror movement
    delay(15);
  }
  delay(1000);

  for (int pos = 180; pos >= 0; pos--) {
    servo1.write(pos);
    servo2.write(180 - pos);
    delay(15);
  }
  delay(1000);
}

Servo Library Details

Library Usage

cpp

#include <Servo.h>  // Built-in library, no installation needed

Key Functions

attach(): Connect servo to pin

cpp

myServo.attach(pin);              // Default pulse width
myServo.attach(pin, min, max);    // Custom pulse width (μs)
// min: 544-1000μs (default 544)
// max: 2000-2400μs (default 2400)

write(): Set servo angle

cpp

myServo.write(angle);  // 0-180 degrees

writeMicroseconds(): Set pulse width directly

cpp

myServo.writeMicroseconds(1500);  // 1000-2000μs typical

read(): Get current angle

cpp

int currentAngle = myServo.read();  // Returns 0-180

attached(): Check if servo is attached

cpp

if (myServo.attached()) {
  // Servo is active
}

detach(): Release servo pin

cpp

myServo.detach();  // Stops servo pulses, saves power

Multiple Servos

•Arduino Uno can control up to 12 servos simultaneously
•All use Timer1
•Pins 9 and 10 lose PWM capability for ALL attached servos
•Use any digital pins, not just PWM pins

Wiring

Standard Servo Wiring

code

Servo Motor    Arduino Uno
-----------    -----------
Signal (Orange/Yellow) → Pin 9 (or other PWM pin)
VCC (Red)      → 5V
GND (Brown/Black) → GND

Power Considerations

⚠️ Important Power Notes:

•
Small servos (SG90, 9g micro):
- •
  Can power from Arduino 5V pin if:
  - •Only 1-2 servos
  - •Not under heavy load
  - •Arduino powered via USB or wall adapter (not battery)
•
Standard servos (SG5010, MG996R):
- •MUST use external power
- •Draw 100-500mA under load
- •Can damage Arduino or brown out if powered from board

•

Proper external power setup:

code

External 5V PSU (1-2A)
├─ VCC → Servo VCC (Red)
└─ GND → Servo GND (Brown) AND Arduino GND (common ground)

Arduino Uno
└─ Pin 9 → Servo Signal (Orange)

•
Common ground is CRITICAL:
- •Always connect Arduino GND to external power supply GND
- •Servo needs common ground for signal reference
•
Capacitor recommendation:
- •Add 100-470μF capacitor across servo power rails
- •Reduces voltage spikes and improves stability

Code Patterns

Smooth Movement

cpp

void moveServoSmooth(int targetPos) {
  int currentPos = myServo.read();
  int step = (targetPos > currentPos) ? 1 : -1;

  for (int pos = currentPos; pos != targetPos; pos += step) {
    myServo.write(pos);
    delay(15);  // Adjust for speed
  }
}

// Usage
moveServoSmooth(180);  // Smooth move to 180°

Non-blocking Movement

cpp

int targetPosition = 90;
int currentPosition = 90;
unsigned long lastMoveTime = 0;
const int moveInterval = 15;  // ms between steps

void loop() {
  unsigned long currentTime = millis();

  if (currentTime - lastMoveTime >= moveInterval) {
    if (currentPosition < targetPosition) {
      currentPosition++;
      myServo.write(currentPosition);
    } else if (currentPosition > targetPosition) {
      currentPosition--;
      myServo.write(currentPosition);
    }
    lastMoveTime = currentTime;
  }

  // Other code runs without blocking
}

Detach to Save Power

cpp

void setup() {
  myServo.attach(servoPin);
  myServo.write(90);
  delay(1000);  // Wait for servo to reach position
  myServo.detach();  // Saves power, servo stops holding position
}

Custom Pulse Width (Calibration)

cpp

// Some servos need custom pulse widths for full range
myServo.attach(9, 1000, 2000);  // Standard servo
myServo.attach(9, 544, 2400);   // Extended range
myServo.attach(9, 700, 2300);   // Custom calibration

// Test and adjust based on your servo's actual range

Continuous Rotation Servos

cpp

#include <Servo.h>

Servo continuousServo;

void setup() {
  continuousServo.attach(9);
}

void loop() {
  continuousServo.write(0);    // Full speed clockwise
  delay(2000);

  continuousServo.write(90);   // Stop
  delay(1000);

  continuousServo.write(180);  // Full speed counter-clockwise
  delay(2000);

  continuousServo.write(90);   // Stop
  delay(1000);
}

Memory Considerations

The Servo library uses:

•~500 bytes of flash memory
•Minimal RAM (a few bytes per servo object)

With Arduino Uno's limited 2KB RAM, avoid:

•Creating excessive servo objects
•Large delays in servo control loops
•Unnecessary String concatenation (use char arrays instead)

Troubleshooting

Servo Jitters or Doesn't Move Smoothly

•Use external power supply for standard servos
•Ensure stable 5V power (not battery near depletion)
•Add capacitor (100-470μF) across servo power
•Check for loose connections
•Avoid using pins 5 or 6 (980Hz PWM causes jitter)

Servo Position Inaccurate

•Calibrate with attach(pin, min, max)
•Try attach(9, 1000, 2000) for standard servos
•Some cheap servos have poor accuracy

Servo Doesn't Reach Full Range (0-180°)

•Adjust pulse width: attach(9, 544, 2400) for extended range
•Some servos are limited to ~160-170° actual range

Multiple Servos Don't Work

•Ensure each servo has its own pin
•Use external power for 3+ servos
•Check common ground connection

Arduino Resets When Servo Moves

•Power issue: Servo drawing too much current
•Use external 5V power supply
•Add capacitor across servo power rails

PWM Doesn't Work on Pins 9 and 10

•Expected behavior: Servo library uses Timer1
•PWM on pins 9 and 10 is disabled when ANY servo is attached
•Use other PWM pins (3, 5, 6, 11) for LED dimming, etc.

Performance Notes

•Servo library uses interrupts for precise timing
•Minimal CPU overhead
•Update rate: ~50Hz (every 20ms)
•Position resolution: 1 degree (0-180)

Additional Resources

See resources/templates/ for more examples.