Temperature Sensor Lm35 Arduino | Sơ Đồ Đấu Nối

LM35 with I2C LCD and Arduino example code

If you want to make a standalone thermometer that doesn’t need a computer, it can be nice to know how to display the temperature readings on an LCD display.

With the example code below, you can display the temperature readings on a 16×2 character I2C LCD.

Connecting the I2C LCD is fairly easy as you can see in the wiring diagram below. You can check out my detailed tutorial on How to control a character I2C LCD with Arduino for more information. If you want to use a standard non-I2C LCD instead, take a look at How to use a 16×2 character LCD with Arduino.

The connections are also given in the table below:

I2C LCD Connections

I2C Character LCD	Arduino
GND	GND
VCC	5 V
SDA	A4
SCL	A5

Note that the LM35 temperature sensor is connected in the same way as before.

Installing the required Arduino libraries

To use an I2C LCD, you need to install the LiquidCrystal_I2C Arduino library.

To install this library, go to Tools > Manage Libraries (Ctrl + Shift + I on Windows) in the Arduino IDE. The Library Manager will open and update the list of installed libraries.

Now search for ‘liquidcrystal_i2c’ and look for the library by Frank de Brabander. Select the latest version and then click Install.

LM35 with I2C LCD example code

/* LM35 analog temperature sensor with I2C LCD and Arduino example code. More info: https://www.makerguides.com */ // Include the required Arduino libraries: #include “LiquidCrystal_I2C.h” // Create a new instance of the LiquidCrystal_I2C class: LiquidCrystal_I2C lcd(0x27, 16, 2); // Degree symbol: byte Degree[] = { B00111, B00101, B00111, B00000, B00000, B00000, B00000, B00000 }; // Define to which pin of the Arduino the output of the LM35 is connected: #define sensorPin A0 void setup() { // Start the LCD and turn on the backlight: lcd.init(); lcd.backlight(); // Create a custom character: lcd.createChar(0, Degree); } void loop() { // Get a reading from the temperature sensor: int reading = analogRead(sensorPin); // Convert the reading into voltage: float voltage = reading * (5000 / 1024.0); // Convert the voltage into the temperature in degree Celsius: float temperature = voltage / 10; // Print the temperature on the LCD; lcd.setCursor(0, 0); lcd.print(“Temperature:”); lcd.setCursor(0, 1); lcd.print(temperature); lcd.write(0); // print the custom character lcd.print(“C”); delay(1000); // wait a second between readings }

You should see the following output on the LCD:

LM35 Temperature Sensor

The LM35 is a low voltage, precision centigrade temperature sensor manufactured by Texas Instruments. It is a chip that provides a voltage output that is linearly proportional to the temperature in °C and is, therefore, very easy to use with an Arduino.

The LM35 temperature sensor is fairly precise, never wears out, works under many environmental conditions and requires no external components to work. In addition, the LM35 sensor does not require calibration and provides a typical accuracy of ±0.5°C at room temperature and ±1°C over a full −55°C to +155°C temperature range.

The sensor can be powered with a 4V to 30V power supply and consumes less than 60µA during active temperature conversions, providing very low self-heating (less than 0.08°C in still air).

Here are the complete specifications:

Power supply	4V to 30V
Current draw	60µA
Temperature range	−55°C to +155°C
Accuracy	±0.5°C
Output scale factor	10mV/°C
Output at 25°C	250mV

For more information, please refer below datasheet.

The only disadvantage of the LM35 sensor is that it requires a negative bias voltage to measure negative temperature. So if you are planning to use the sensor to measure negative temperature, it is recommended that you use TMP36 temperature sensor. The TMP36 by Analog Devices is fairly accurate (-40°C to 125°C) and has the advantage of being able to measure negative temperatures without the need for negative bias voltage. You can find a dedicated tutorial for the TMP36 below.

A better alternative to the LM35 is to use a digital temperature sensor like the DS18B20 which comes in the same package. Digital temperature sensors have better noise immunity which is useful when the sensor is placed at a distance or in an electrically noisy environment.

LM35 analog temperature sensor with Arduino example code

With the following example code, you can read the temperature from an LM35 sensor and display it in the Serial Monitor.

You can upload the example code to your Arduino using the Arduino IDE.

/* LM35 analog temperature sensor with Arduino example code. More info: https://www.makerguides.com */ // Define to which pin of the Arduino the output of the LM35 is connected: #define sensorPin A0 void setup() { // Begin serial communication at a baud rate of 9600: Serial.begin(9600); } void loop() { // Get a reading from the temperature sensor: int reading = analogRead(sensorPin); // Convert the reading into voltage: float voltage = reading * (5000 / 1024.0); // Convert the voltage into the temperature in degree Celsius: float temperature = voltage / 10; // Print the temperature in the Serial Monitor: Serial.print(temperature); Serial.print(” \xC2\xB0″); // shows degree symbol Serial.println(“C”); delay(1000); // wait a second between readings }

You should see the following output in the Serial Monitor:

Make sure that the baud rate of the Serial Monitor is also set to 9600.

How the code works

First, I defined to which pin of the Arduino the VOUT pin of the sensor is connected. In this case, we used the analog pin A0. The statement #define can be used to give a name to a constant value. The compiler will replace all references to this constant with the defined value when the program is compiled. So everywhere you mention

sensorPin

, the compiler will replace it with A0 when the program is compiled.

// Define to which pin of the Arduino the output of the LM35 is connected: #define sensorPin A0

In the setup section of the code, we begin serial communication at a baud rate of 9600.

void setup() { // Begin serial communication at a baud rate of 9600: Serial.begin(9600); }

In the loop section of the code, we start by taking a reading from the sensor with the function

analogRead(pin)

.

// Get a reading from the temperature sensor: int reading = analogRead(sensorPin);

Next, we use the formulas that I mentioned earlier in the article to convert the reading into voltage and then into temperature.

// Convert the reading into voltage: float voltage = reading * (5000 / 1024.0); // Convert the voltage into the temperature in degree Celsius: float temperature = voltage / 10;

Lastly, the results are printed in the Serial Monitor:

// Print the temperature in the Serial Monitor: Serial.print(temperature); Serial.print(” \xC2\xB0″); // shows degree symbol Serial.println(“C”);

Arduino Code – Simple Thermometer

The following sketch shows a quick way to read LM35 temperature sensor and can serve as the basis for more practical experiments and projects. It simply reads the value from the LM35 using analog port A0 and prints the current temperature (in both °C and °F) on the serial monitor. Go ahead and upload it to your Arduino.


// Define the analog pin, the LM35's Vout pin is connected to #define sensorPin A0 void setup() { // Begin serial communication at 9600 baud rate Serial.begin(9600); } void loop() { // Get the voltage reading from the LM35 int reading = analogRead(sensorPin); // Convert that reading into voltage float voltage = reading * (5.0 / 1024.0); // Convert the voltage into the temperature in Celsius float temperatureC = voltage * 100; // Print the temperature in Celsius Serial.print("Temperature: "); Serial.print(temperatureC); Serial.print("\xC2\xB0"); // shows degree symbol Serial.print("C | "); // Print the temperature in Fahrenheit float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0; Serial.print(temperatureF); Serial.print("\xC2\xB0"); // shows degree symbol Serial.println("F"); delay(1000); // wait a second between readings }


You should see the following output in the serial monitor.

Code Explanation:

The sketch starts by defining the Arduino pin to which the sensor’s Vout pin is connected.


#define sensorPin A0


In the setup, we initialize the serial connection with the computer.


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


In the loop, we first read in the analog signal from the LM35 using the

analogRead()

function.


int reading = analogRead(sensorPin);


Next, we will use the formulas we discussed earlier in the article to convert the analog reading into voltage and then into temperature.


float voltage = reading * (5.0 / 1024.0); float temperatureC = voltage * 100;


Next, the results are printed on the Serial Monitor.


Serial.print("Temperature: "); Serial.print(temperatureC); Serial.print("\xC2\xB0"); // shows degree symbol Serial.print("C | ");


The temperature value we get is in Celsius (°C). It is converted in to Fahrenheit (°F) using a simple formula and printed on the Serial Monitor.

T(°F) = T(°C) × 9/5 + 32


float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0; Serial.print(temperatureF); Serial.print("\xC2\xB0"); // shows degree symbol Serial.println("F");


Improve the precision of the readings

Because we used the default reference voltage of the Arduino for analog input (i.e. the value used as the top of the input range), the maximum resolution we get from the ADC is 5000/1024 = 4.88 mV or 0.49°C.

If we want a higher precision, we can use the built-in 1.1 V reference from the Arduino instead. This reference voltage can be changed using the function analogReference().

With 1.1 V as the reference voltage, we get a resolution of 1100/1024 = 1.07 mV or 0.11°C. Note that this limits the temperature range that we can measure to 0 to 110 degrees Celsius.

I have highlighted the lines you need to add/change in the code below:

/* LM35 analog temperature sensor with Arduino example code. More info: https://www.makerguides.com */ // Define to which pin of the Arduino the output of the LM35 is connected: #define sensorPin A0 void setup() { // Begin serial communication at a baud rate of 9600: Serial.begin(9600); // Set the reference voltage for analog input to the built-in 1.1 V reference: analogReference(INTERNAL); } void loop() { // Get a reading from the temperature sensor: int reading = analogRead(sensorPin); // Convert the reading into voltage: float voltage = reading * (1100 / 1024.0); // Convert the voltage into the temperature in degree Celsius: float temperature = voltage / 10; // Print the temperature in the Serial Monitor: Serial.print(temperature); Serial.print(” \xC2\xB0″); // shows degree symbol Serial.println(“C”); delay(1000); // wait a second between readings }

Sơ đồ đấu nối

Arduino Uno	Cảm biến nhiệt độ LM35
VCC	+Vs (4 – 20V)
GND	GND
A0	VOUT

Các linh kiện cần thiết cho dự án

Tên linh kiện	Số lượng	Shopee
Arduino Uno R3	Mua ngay
Dây cáp nạp	Mua ngay
Cảm biến nhiệt LM35	Mua ngay
Breadboard (Bo test)	Mua ngay
Dây cắm (Đực – Đực)	Mua ngay

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How to Measure Temperature

The LM35 is easy to use; just connect the left pin to power (4V to 30V) and the right pin to ground (assuming the flat side of the sensor is facing you). Then the middle pin will have an analog voltage that is directly proportional (linear) to the temperature in °C. This can be easily seen in the output voltage vs temperature characteristic. Note that the analog output voltage is independent of the power supply.

To convert the voltage to temperature, simply use the basic formula:

Temperature (°C) = Vout * 100

For example, if the voltage out is 0.5V that means that the temperature is 0.5 * 100 = 50 °C

Connecting the LM35 Temperature Sensor to an Arduino

Hooking up the LM35 to an Arduino is super simple. You only need to connect three pins: two for power and one for reading the sensor value.

The sensor can be powered from 5V. The positive voltage connects to ‘+Vs’ and ground connects to ‘GND‘. The middle pin ‘Vout’ is the analog signal output from the sensor and connects to the A0 analog input of an Arduino.

Below is the hookup for the experiments with the LM35:

To measure air temperature leave the sensor in the open air or attach it to an object you want to measure the temperature of, such as a heat sink.

Code mẫu

int sensorPin = A0; void setup() { Serial.begin(9600); } void loop() { int reading = analogRead(sensorPin); float voltage = reading * 5.0 / 1024.0; float temp = voltage * 100.0; Serial.println(temp); delay(1000); }

Giải thích Code

reading = analogRead(sensorPin);

Hàm

analogRead()

có nhiệm vụ đọc giá trị điện áp từ một chân Analog (ADC), hàm này luôn trả về 1 số nguyên nằm trong khoảng từ 0 đến 1023 tương ứng với thang điện áp (mặc định) từ 0 đến 5V. Hàm

analogRead()

cần 100 micro giây để thực hiện.

• Xem bài viết kiểu số nguyên int để hiểu thêm.

Vậy

reading = analogRead(sensorPin)

có nghĩa là đọc giá trị điện áp từ cảm biến nhiệt độ LM35.

float voltage = reading * 5.0 / 1024.0;

Công thức tính ra giá trị hiệu điện thế từ giá trị cảm biến (đơn vị Volt) Voltage = giá trị điện áp từ cảm biến chia cho mức analog cao nhất (1024) rồi nhân với mức điện áp 5V.

Như ở trên ta thấy nhiệt độ thay đổi tuyến tính 10mV/°C nên đổi từ Vol sang °C thì ta chỉ cần nhân giá trị điện thế với 100 là ra nhiệt độ.

float temp = voltage * 100.0;