Arduino Sensor Projects: Servo Motor & Temperature Sensor for Beginners

A servo motor is controlled with Arduino using the built-in Servo library, which sends a PWM signal to rotate the motor to a specific angle (0°–180°) using a single signal wire, while a temperature sensor like the LM35 or DHT11 is read using an analog or digital pin to report temperature in real time on the Serial Monitor or an LCD. Both are among the most common first “sensor + actuator” projects for students because they use only three to four wires, require no external library beyond what Arduino IDE includes or offers through the Library Manager, and directly demonstrate the read-input/control-output logic that underlies most embedded systems coursework.

Key takeaways

• A standard hobby servo motor rotates between 0° and 180°, controlled by a PWM signal on one wire.
• Servos need a separate 5V power source for anything beyond a single small servo powering multiple servos directly from the Arduino’s 5V pin can cause voltage drops and erratic behavior.
• LM35 is an analog temperature sensor (reads a voltage that scales linearly with °C); DHT11 is a digital sensor (reads temperature and humidity together via a single data pin).
• Both projects use different Arduino pin types: servo uses a PWM digital pin, LM35 uses an analog pin, DHT11 uses any digital pin (via library).

Project 1: Controlling a servo motor with Arduino

Components needed

Component	Quantity	Notes
Arduino Uno (or Nano)	1	Any PWM-capable digital pin works
SG90 (or similar) micro servo	1	Standard 3-wire hobby servo
Jumper wires	3	Signal, power, ground
External 5V power (for multiple servos)	Optional	Not needed for a single small SG90 servo

Wiring diagram

Servo Wire	Color (typical)	Connects to
Signal	Orange/Yellow	Arduino digital PWM pin (e.g., pin 9)
Power (+)	Red	Arduino 5V
Ground (−)	Brown/Black	Arduino GND

Arduino code: sweep servo 0°–180°

cpp

#include <Servo.h>

Servo myServo;

void setup() {
  myServo.attach(9); // Signal wire connected to pin 9
}

void loop() {
  for (int angle = 0; angle <= 180; angle++) {
    myServo.write(angle);
    delay(15);
  }
  for (int angle = 180; angle >= 0; angle--) {
    myServo.write(angle);
    delay(15);
  }
}

What each key function does:

• myServo.attach(9) tells the library which pin sends the PWM control signal.
• myServo.write(angle) rotates the servo shaft to the specified angle (0–180°).
• The two for loops sweep the servo smoothly from 0° to 180° and back, with a 15ms delay between each degree of movement.

Common servo problems and fixes

Problem: Servo jitters or moves erratically
Fix: This is almost always a power issue the Arduino’s 5V pin cannot supply enough current for the servo’s movement spikes. Use a separate 5V power supply for the servo, with a shared ground between it and the Arduino.

Problem: Servo doesn’t reach full 0°–180° range
Fix: Some servos have a narrower usable range; use myServo.writeMicroseconds() instead of write() for finer control, adjusting the pulse width (typically 500–2500 microseconds) to match your specific servo’s range.

Project 2: Reading temperature with Arduino

Components needed

Component	Quantity	Notes
Arduino Uno (or Nano)	1	Any analog pin (LM35) or digital pin (DHT11) works
LM35 temperature sensor OR DHT11 sensor	1	LM35 = analog, simpler; DHT11 = digital, adds humidity
10kΩ resistor	1 (DHT11 only)	Pull-up resistor for DHT11 data line
Jumper wires	3	Power, ground, signal

Wiring diagram (LM35 analog method)

LM35 Pin	Connects to
VCC	Arduino 5V
GND	Arduino GND
Output (Vout)	Arduino analog pin A0

Arduino code: LM35 temperature reading

cpp

const int sensorPin = A0;

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

void loop() {
  int rawValue = analogRead(sensorPin);
  float voltage = rawValue * (5.0 / 1023.0);
  float temperatureC = voltage * 100; // LM35: 10mV per °C

  Serial.print("Temperature: ");
  Serial.print(temperatureC);
  Serial.println(" °C");

  delay(1000);
}

What each key line does:

• analogRead(sensorPin) reads the raw analog value (0–1023) representing 0–5V.
• voltage = rawValue * (5.0 / 1023.0) converts the raw value into an actual voltage.
• temperatureC = voltage * 100 converts voltage to °C, since the LM35 outputs exactly 10mV per degree Celsius.

Wiring diagram (DHT11 digital method)

DHT11 Pin	Connects to
VCC	Arduino 5V
GND	Arduino GND
Data	Arduino digital pin 2 (with 10kΩ pull-up resistor to 5V)

Arduino code: DHT11 temperature + humidity reading

cpp

#include <DHT.h>

#define DHTPIN 2
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

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

void loop() {
  float temperature = dht.readTemperature();
  float humidity = dht.readHumidity();

  if (isnan(temperature) || isnan(humidity)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.print(" °C  Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");

  delay(2000);
}

Note: the DHT.h library must be installed first via Tools → Manage Libraries → search “DHT sensor library” by Adafruit.

LM35 vs DHT11: which should you use?

Feature	LM35	DHT11
Reads	Temperature only	Temperature + humidity
Signal type	Analog	Digital (single-wire protocol)
Accuracy	±0.5°C, more precise	±2°C, less precise
Reading speed	Instant	~1 reading per second (slower)
Extra library needed	No	Yes (DHT library)
Best for	Precise, temperature-only projects	Weather stations, humidity-dependent projects

Combining both projects: a servo-controlled fan/vent concept

A common next-step student project combines these two: read temperature with an LM35 or DHT11, then use the reading to control a servo (e.g., opening a vent flap when temperature crosses a threshold):

cpp

#include <Servo.h>

Servo myServo;
const int sensorPin = A0;

void setup() {
  myServo.attach(9);
  Serial.begin(9600);
}

void loop() {
  int rawValue = analogRead(sensorPin);
  float temperatureC = (rawValue * (5.0 / 1023.0)) * 100;

  if (temperatureC > 30.0) {
    myServo.write(90); // Open vent
  } else {
    myServo.write(0);  // Close vent
  }

  Serial.println(temperatureC);
  delay(1000);
}

This pattern read sensor, compare threshold, drive actuator is the basis for most automation and IoT lab projects.

Frequently asked questions