LM35 vs DS18B20: How to Choose the Right Temperature Sensor for Your Project?

Contents List

• Introduction of Temperature Sensors.
• Types of Temperature Sensors.
• Semiconductor Sensors.
• LM35 Temperature Sensor.
  • What Is the LM35?
  • LM35 Package Types.
  • LM35 Pinout.
  • Internal Circuitry of the LM35.
  • How Does the LM35 Work?
  • LM35 Specifications.
  • Equivalents & Alternatives for LM35.
  • Advantages of the LM35.
  • Limitations of the LM35.
  • Common Applications of the LM35.
  • Interfacing LM35 with Arduino.
  • Arduino Example  – Reading Temperature with LM35.
  • Practical Projects using LM35.
• DS18B20 Temperature Sensor.
  • What Is the DS18B20 ?
  • DS18B20 Package Types.
  • DS18B20 Pinout.
  • Internal Circuitry of the DS18B20.
  • DS18B20 Power Modes.
  • How Does the DS18B20 Work?
  • DS18B20 Specifications.
  • Equivalents & Alternatives of DS18B20.
  • Advantages of the DS18B20.
  • Limitations of the DS18B20.
  • Common Applications of the DS18B20.
  • Interfacing DS18B20 with Arduino.
  • Example waterproof DS18B20 probe with Arduino.
  • Practical projects Using DS18B20.
• Comparisons between LM35 and DS18B20.
• Frequently Asked Questions.
• Conclusion.

Reading Time Approximately is 20 minute 

Introduction of Temperature Sensors

Temperature is the most often-measured environmental quantity. This might be expected since most physical, electronic, chemical, mechanical, and biological systems are affected by temperature. Certain chemical reactions, biological processes, and even electronic circuits perform best within limited temperature ranges. Temperature is one of the most commonly measured variables and it is therefore not surprising that there are many ways of sensing it. Temperature Sensing can be done either through direct contact with the heating source or remotely, without direct contact with the source using radiated energy instead. There are a wide variety of temperature sensors on the market today, including Thermocouples, Resistance Temperature Detectors (RTDs), Thermistors, Infrared and Semiconductor Sensors.

A precision IC Temperature Sensor is a solid-state, small device that measures temperature with a two-terminal IC, generating an output voltage or current that is proportional to the total temperature. These temperature sensor ICs are mainly designed to measure temperature because they usually work as a voltage output or temperature-dependent current source, with the output signal directly associated with the measured temperature. Examples of these temperature sensor ICs are: LM34 IC, the LM35 IC, and Other IC sensors. This article elaborates on the LM35 sensor IC, its working, and its applications.

Types of Temperature Sensors

• Thermocouple.
• RTD.
• Thermistors.
• Semiconductor Sensors.

Semiconductor Sensors

Temperature sensors can be classified basically under two categories: analog and digital, with the measure of temperature that both of them obtain certainly differing. However, these temperature detectors differ considerably in their working, output, and applications.

Analog Temperature Sensors:

• Output: Produces a continuous signal (voltage or current) proportional to the measured temperature.
• Working: Requires additional circuitry, such as amplifiers and ADCs, to process the signal.
• Accuracy: This may require frequent calibration to maintain accuracy.
• Applications: Common in simple systems where digital processing is unnecessary.

 Digital Temperature Sensors:

• Output: Provides a digital signal that can be directly processed by microcontrollers or computers.
• Working: Integrates ADC and signal processing within the sensor, reducing the need for external components.
• Accuracy: Offers high precision and stability with built-in calibration features.
• Applications: Used in advanced systems requiring precise and reliable temperature monitoring, such as IoT Devices, Medical equipment, and Automotive systems.

LM35 Temperature Sensor

What Is the LM35?

The LM35 is a precision analog temperature sensor designed to measure temperature directly in degrees Celsius. It produces an analog output voltage that changes linearly with the measured temperature, making it easy to interface with microcontrollers such as Arduino and other development boards.

Unlike a digital temperature sensor, the LM35 does not send temperature data through a communication protocol. Instead, its Vout pin generates a voltage proportional to the temperature. The sensor has a sensitivity of approximately 10 mV/°C, meaning that the output voltage increases by about 10 mV for every 1°C increase in temperature.

This simple voltage-to-temperature relationship makes the LM35 particularly useful for beginners learning about analog sensors, ADCs, and microcontroller-based measurement systems.

LM35 Package Types

The LM35 is available in several package shapes, depending on the specific LM35 variant:

LM35 Pinout

Although the LM35 looks like a simple three-pin transistor-style component, it contains several functional circuits inside its package.

Temperature-Sensitive Circuit

The sensing section uses semiconductor junction characteristics that vary with temperature. These changes provide the electrical information required to determine the temperature.

Differential Amplifier

The internal amplifier processes the small temperature-dependent signal and helps produce the sensor’s linear output.

Voltage Reference and Calibration Circuitry

Internal circuitry establishes the appropriate operating point and helps maintain the specified temperature-to-voltage relationship.

Output Buffer

The output stage provides the analog signal at the Vout pin and allows the sensor to interface with an analog input of a microcontroller.

The internal design allows the LM35 to provide a factory-calibrated output without requiring the user to perform a separate calibration procedure for normal applications.

How Does the LM35 Work?

LM35 sensor works on the diode principle, which means that whenever the temperature increases, the voltage across a diode will increase at a known rate. So, by accurately amplifying the change in voltage, it is simple to produce an analog signal that is directly proportional to temperature. The internal structure of the LM35 sensor is shown below.                                                                              This sensor includes two transistors, where one transistor has 10 times the emitter region of the other. So it has one-tenth of the current supply density, as a similar current is flowing throughout both transistors. This causes a voltage supply across the R1 resistor that is proportional to the total temperature.

This IC has an amplifier located at the top side, which ensures the voltage supply at the base terminal of the left Q1 transistor is proportional to the total temperature by comparing the two transistors’ output. So the right-side amplifier changes the total temperature into either Celsius or Fahrenheit.

For every 1°C increase in temperature, the Vout pin produces exactly 10mV higher output. This makes the relationship between temperature and voltage very straightforward:

Output Voltage = Temperature (°C) × 10mV

For example:

At 0°C → Output = 0mV
At 25°C → Output = 250mV
At 100°C → Output = 1000mV (1V)
Since the output is a clean analog voltage, a microcontroller like Arduino simply reads it through an ADC (Analog to Digital Converter) pin and converts it back to a temperature value using a simple formula.

LM35 Specifications

Note:

These values are based on the technical information presented in the Pinout Hub reference; for production designs, the exact part-number datasheet should be used as the final authority.

Equivalents & Alternatives for LM35

Equivalent LM35 sensors are:

LM34, DS1620, DS18B20, LM94022, etc.

Alternative temperature sensors are:

DHT11, LM35, DHT22, DS18B20, BMP180, BME280, etc.

Advantages of the LM35

• Linear output: The output voltage changes predictably with temperature.
• Simple interface: It can be connected directly to an analog input.
• Low current consumption: Typical current consumption is around 60 µA.
• Wide measurement range: Suitable for temperatures from −55°C to +150°C.
• Easy temperature conversion: The 10 mV/°C sensitivity makes calculations straightforward.
• Low self-heating: Low power consumption helps minimize the sensor’s influence on the measured temperature.
• Compact package: Available in several small package options.

Limitations of the LM35

• The LM35 is a simple and useful sensor, but its analog output also introduces some considerations.
• Because the temperature information is transmitted as a voltage, the reading can be affected by the microcontroller’s ADC resolution, reference voltage, electrical noise, and wiring. The source document also identifies limited resolution, relatively slow response, and susceptibility to noise as potential disadvantages.
• For applications that require digital communication, advanced diagnostics, or multiple sensors sharing a single data line, a digital temperature sensor such as the DS18B20 may be more suitable.

Common Applications of the LM35

The LM35 can be used in many applications where temperature needs to be measured or monitored.

• Ambient temperature monitoring.
• Arduino and microcontroller projects.
• HVAC temperature monitoring and control.
• Industrial process monitoring.
• Laboratory temperature measurement.
• Battery temperature monitoring.
• Electronic equipment thermal monitoring.
• Automotive temperature monitoring.
• Food-processing temperature monitoring.
• Temperature-controlled systems.
• Thermal protection and shutdown circuits.

Interfacing LM35 with Arduino

The LM35 can be easily connected to an Arduino Uno because the Arduino provides analog input pins that can measure the sensor’s output voltage.

A basic connection is:

The Arduino reads the analog voltage on A0 using its ADC. The measured voltage can then be converted into temperature using the LM35’s 10 mV/°C sensitivity.

For example, if the Arduino measures approximately 0.25 V:

Temperature = 0.25 V ÷ 0.010 V/°C = 25°C

This makes the LM35 a useful component for learning how an analog sensor communicates information to a microcontroller.

Arduino Example – Reading Temperature with LM35

In this example, we’re going to read temperature data from the LM35 sensor and display the results in both degrees Celsius (°C) and degrees Fahrenheit (°F) on the Serial Monitor.

// 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
  // Replace 5.0 with 3.3, if you are using a 3.3V Arduino
  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("°C  |  ");

  // Print the temperature in Fahrenheit
  float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;
  Serial.print(temperatureF);
  Serial.println("°F");

  delay(1000);  // wait a second between readings
}

#define sensorPin A0

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

int reading = analogRead(sensorPin);

float voltage = reading * (5.0 / 1024.0);

float temperatureC = voltage * 100;

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

float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;
Serial.print(temperatureF);
Serial.println("°F");

DS18B20 Temperature Sensors

What Is the DS18B20?

The DS18B20 digital thermometer provides 9-bit to 12-bit temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points.

The DS18B20 communicates over a 1-Wire® bus that requires only one data line (and ground) for communication with microcontroller. In addition, the DS18B20 can derive power directly from the data line (“parasite power”), eliminating the need for an external power supply.

Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-Wire bus. Thus, it is simple to use one microcontroller to control many DS18B20s distributed over a large area.

Applications that can benefit from this feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment, or machinery.

DS18B20 Package Types

The DS18B20 is available in several package shapes, depending on the specific DS18B20 variant:

DS18B20 Pinout

Internal Circuitry of the DS18B20

How Does the DS18B20 Work?

The read and write sequence and temperature measurement principle of DS18B20 are the same as DS1820. Only the number of digits of the temperature value obtained varies with the resolution. And the delay time during temperature conversion is reduced from 2s to 750ms.

DS18B20 Temperature Measurement Principle Diagram

The oscillation frequency of the crystal oscillator with low temperature coefficient in the picture is little affected by temperature. It is used to generate a fixed frequency pulse signal and send it to the subtraction counter 1.

The high temperature coefficient crystal oscillator changes its oscillation frequency significantly with temperature changes. At the same time, the generated signal is used as the pulse input of the subtraction counter 2.

The figure also implies a counting gate. When the counting gate is opened, DS18B20 counts the clock pulses generated by the low temperature coefficient oscillator to complete the temperature measurement.

The opening time of the counting gate is determined by the high temperature coefficient oscillator. Before each measurement, first put the base corresponding to -55 ℃ into the subtraction counter 1 and the temperature register respectively. The subtraction counter 1 and the temperature register are preset to a base value corresponding to -55 ℃.

The subtraction counter 1 subtracts the pulse signal generated by the low temperature coefficient crystal oscillator. When the preset value of the subtraction counter 1 is reduced to 0, the value of the temperature register will increase by 1, the preset of the subtraction counter 1 will be reloaded, and the subtraction counter 1 will restart counting the pulse signals generated by the low temperature coefficient crystal oscillator.

This loop until the subtraction counter 2 counts to 0, stop the accumulation of the temperature register value. The value in the temperature register is the measured temperature at this time.

The slope accumulator is used to compensate and correct the nonlinearity in the temperature measurement process, and its output is used to correct the preset value of the subtraction counter.

As long as the counting gate is not closed, repeat the above process until the temperature register value reaches the measured temperature value. This is the temperature measurement principle of DS18B20.

In addition, because the DS18B20 single-wire communication function is completed in time sharing, it has a strict concept of time slots. Therefore, the read and write timing is very important. Various operations of the system to DS18B20 must be carried out according to the agreement.

The operating protocol is:

initialize DS18B20 (send reset pulse) → send ROM function command → send memory operation command → process data. The timing diagram of various operations is the same as that of DS1820.

DS18B20 Specifications

Equivalents & Alternatives of DS18B20

DS18B20 temperature sensor equivalent is DS18S20:

So alternative temperature sensors are

TMP100, Thermocouple, LM75, SHT15, DHT11, TPA81, LM35DZ, D6T, etc.

Advantages of the DS18B20

The advantages of the DS18B20 temperature sensor include the following:

• DS18B20 temperature sensors are small in size.
• These are durable.
• It has a metal covering that protects the sensor from heat & water.
• Multiple sensors can be connected on a similar bus.
• This sensor is easily integrated into a variety of systems.
• It has a user-configurable resolution.
• It provides precise and reliable temperature data for different applications.

Limitations of the DS18B20

Limitations of the DS18B20 temperature sensor include the following:

• This temperature sensor is expensive.
• It takes much time to complete a reading.
• It may not be available with comprehensive packaging, thus you may require using external circuits to work it.
• Data transmission delay occurs.
• Its temperature range is limited ranges from -55°C to 125°C.

Common Applications of the DS18B20

The applications of the DS18B20 temperature sensor include the following:

• The DS18B20 temperature sensor measures the temperature within rigid environments like soil, chemical solutions, mines, and more.
• Users apply it to measure liquid temperature.
• Industries employ it in thermostat control systems as a temperature-measuring device.
• This sensor finds use wherever individuals need to calculate temperature at several points.
• Industrial systems utilize this sensor to measure the temperature of machinery, processes, equipment, and so on.
• Manufacturers use it in consumer products to measure temperature.
• HVAC systems utilize it to measure temperature within buildings, mainly for their controls.
• Thermometers, thermostatic controls, thermally sensitive systems, harsh environments, and Hydro-projects use this temperature sensor.
• Industries use this sensor for temperature measurement, environmental sensing, liquid temperature monitoring, weather stations, and HVAC environmental controls.

Interfacing DS18B20 with Arduino

Let’s learn how to connect the DS18B20 temperature sensor to an Arduino.

The wiring is pretty simple. First, connect the VDD pin of the sensor to the 5V pin on your Arduino. Next, connect the GND (ground) pin of the sensor to any of the Arduino’s GND pins.

For the data connection, connect the sensor’s DQ (data) pin to digital pin 2 on the Arduino. To ensure the data signal remains stable, you’ll need to add a 4.7k ohm pull-up resistor between the DQ pin and the 5V power pin. (Note: the Arduino’s internal pull-up resistors won’t work for this, so you need to use an external one.)

Parts Required

To show you how the sensor works, we’ll build a simple example that reads the temperature from the DS18B20 sensor with the Arduino and displays the values on the Arduino Serial Monitor.

Here’s a list of parts you need to complete this tutorial

• Arduino UNO – read Best Arduino Starter Kits
• DS18B20 temperature sensor (one or multiple sensors) – waterproof version
• 4.7k Ohm resistor
• Breadboard
• Jumper wires

Here’s a quick reference table for the pin connections:

If you’re using the waterproof DS18B20 probe, the wires are color-coded: Connect the red wire to the Arduino’s 5V pin, the black wire to GND, and the yellow wire to digital pin 2.

Just like before, don’t forget to add a 4.7k ohm resistor between the yellow wire (data) and the red wire (power) to keep the communication stable.

Example waterproof DS18B20 probe with Arduino

As from the above schematic diagram the VCC and GND of sensor are connected to 5V and GND of Arduino, and DATA pin is connected to pin 7 of Arduino. A 4.7k Ohm pull up resister is connected to data pin from 5V supply for stable data communication.

After connecting all the required components according to the above circuit diagram, we need to upload the code into the Arduino through Arduino IDE.

Setting for the Pull-up Register/Pull-down Register Selection Jumpers When connect DS18B20 with the adapter, please choose to use the Pull-up Register Jumper

Sample Code

/***************************************************************/
 Insturciton:
 Connection:
 1.Plugable Terminal Sensor Adapter & Waterproof DS18B20 Digital Temperature Sensor
                 A   ---->     Blue(DATA SIGNAL)
                 B   ---->     RED   (VIN)
                 C   ---->     Black (GND)

 2.Waterproof DS18B20 Digital Temperature Sensor & Arduino board
              1(A)   ---->     Digital Pin2
              2(B)   ---->     5V/3.3V
              3(C)   ---->     GND

 Setting for the Pull-up Register/Pull-down Register Selection Jumpers
     When connect DS18B20 with the adapter,please choose to use the
     Pull-up Register Jumper
 ***************************************************************/
#include <OneWire.h>

int DS18S20_Pin = 2; //DS18S20 Signal pin on digital 2

//Temperature chip i/o
OneWire ds(DS18S20_Pin);  // on digital pin 2

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

Practical projects Using DS18B20

Comparisons between LM35 and DS18B20

Frequently Asked Questions

Why does my LM35 give incorrect temperature readings?

The most common cause of inaccurate LM35 readings is electrical noise on the analog input. To improve accuracy: (1) use a short wire between LM35 and Arduino, (2) add a 100nF decoupling capacitor between the LM35’s VCC pin and GND as close to the chip as possible, (3) average multiple readings (analogRead() called 10 times, sum divided by 10), and (4) switch to the Arduino’s internal 1.1V reference for better ADC resolution at room temperature.

Can I use the DHT11 outdoors?

The DHT11 is not rated for outdoor use. Its temperature range of 0–50°C means it will not work in winter conditions that go below zero, and its plastic housing is not sealed against moisture or rain. For outdoor use, the DS18B20 waterproof probe is a much better choice. If you need humidity outdoors, the SHT31 or BME280 in a waterproof enclosure is the professional approach.

How many DS18B20 sensors can I connect to one Arduino pin?

Theoretically, you can connect up to 127 DS18B20 sensors on a single Arduino pin using the 1-Wire bus (each has a unique 64-bit address). In practice, beyond 10–15 sensors on a long bus you may encounter timing and signal integrity issues. For very long cable runs or many sensors, use a separate 4.7kΩ pull-up per sensor branch and keep wire lengths under 100m. The DallasTemperature library handles all addressing and multi-sensor reading automatically.

What is the difference between DHT11 and DHT22?

The DHT22 (also called AM2302) is the upgraded version of the DHT11. The DHT22 offers better temperature accuracy (±0.5°C vs ±2°C), wider temperature range (-40°C to +80°C vs 0°C to 50°C), better humidity range (0–100% RH vs 20–90% RH), and higher resolution (0.1°C vs 1°C). The DHT22 costs approximately 2–3x more than the DHT11. For serious projects, the DHT22 is worth the price difference. The code for both is identical in the Adafruit DHT library — just change DHT11 to DHT22.

Can I use these sensors with ESP8266 or ESP32 instead of Arduino?

Yes, all three sensors work perfectly with ESP8266 and ESP32 as well. The same libraries (DHT, OneWire, DallasTemperature) are fully compatible. The ESP8266 and ESP32 operate at 3.3V logic — the LM35 should be powered from the 3.3V pin (adjust the millivolt calculation accordingly), while the DHT11 and DS18B20 work fine at both 3.3V and 5V. ESP32 is the preferred choice for IoT temperature logging projects since it has built-in Wi-Fi and Bluetooth.

Conclusion

Choosing between the LM35 and DS18B20 depends on the requirements of your project. The LM35 is a simple, low-cost analog temperature sensor that provides a voltage output proportional to temperature, making it a good choice for basic Arduino and analog measurement projects. The DS18B20, on the other hand, provides digital temperature readings, better wiring flexibility through its 1-Wire interface, and supports multiple sensors on the same data line.

For simple and low-cost temperature measurement, the LM35 is an excellent option. If your project requires digital communication, multiple sensors, longer wiring, or easier integration with microcontrollers, the DS18B20 is generally the better choice.

Ultimately, there is no single sensor that is best for every application. Consider your project’s accuracy requirements, wiring distance, number of sensors, microcontroller compatibility, and software needs before making your choice.