LM35 Sensor : PinOut, Features, Specifciations, Interfacing, Working & Its Applications

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.

What is an LM35 Sensor?

LM35 is an analog and linear temperature sensor from National Semiconductors that provides an analog signal that is proportional to the temperature. So the output voltage can be easily understood to get a temperature reading in Celsius. This sensor can be operated with a 5V supply & the standby current of this sensor is < 60uA. The sensitivity of this sensor is 10mV for each degree Celsius; thus, the output voltage will increase when the temperature increases. This temperature sensor is used to measure nearby temperature, which ranges from -55 °C to 150 °C. So this sensor provides more precise temperature output as compared to thermistor output.

LM35 Sensor Working

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. The small circle (i) in the structure is a constant current source.

The two resistors in the structure can be calibrated in the factory to generate a highly precise temperature sensor. This IC includes many transistors within it, where two transistors are in the center and some transistors are in every amplifier, constant current source, and curvature compensation circuit. All these can be arranged into a small package using three terminals.

LM35 Sensor Pin Diagram:

The diagram below shows the pin configuration of the LM35 sensor. This sensor IC includes three terminals, which are discussed below.

• Pin-1 (Vcc): This power supply pin connects to +5V.
• Pin-2 (Vout): This output pin must connect to the microcontroller’s analog pin.
• Pin-3 (Ground): This ground pin connects to 0V/GND.

Features & Specifications:

The features and specifications of the LM35 sensor include the following.

• LM35 is a temperature sensor.
• This sensor includes three pins.
• Its input voltage ranges from -2 V to 35 V, but it normally operates at 5V.
• This sensor is available in different packages, like TO-92, TO-CAN, SO IC, TO-220, etc.
• Its Output voltage is directly proportional to temperature; thus, there is an increase of 10mV for each 1°C increase in temperature.
• Its Drain current is < 60 uA.
• This sensor is small and not expensive, thus suitable mainly for remote applications.
• Calibration accuracy will be ±0.5°C at room temperature.
• The current consumption is 60 µA.
• It has low self-heating characteristics, which reduces the sensor’s temperature and affects the measured temperature.
• Its measured temperature ranges from -55°C to 150°C.

Equivalents & Alternatives

Equivalent LM35 sensors are; LM34, DS1620, DS18B20, LM94022, etc. Alternative temperature sensors are; DHT11, LM35, DHT22, DS18B20, BMP180, BME280, etc.

LM35 Sensor Interfacing with Arduino

The LM35 sensor’s interfacing with Arduino is shown below. The required components to make this interfacing mainly include Arduino Uno, an LM35 sensor, and connecting wires. The connections of this simple interfacing follow as;

• Connect the 5V power pin of the Arduino to the Vcc pin of the LM35 sensor.
• The Arduino’s A0 pin is connected to the output pin of the sensor.
• Connect the GND pin of the Arduino to the GND pin of the LM35 sensor.

Code:

Once the above connections are made for interfacing, you have to write the required code to change the sensor’s output voltage to temperature data. So for that, you have to change the values of ADC to voltage. After that, this voltage must be multiplied by 10 to get the output in temperature.

// LM35 is connected to this PIN
#define sensorPin A0
void setup() {
// Init serial at 9600 baud
Serial.begin(9600);
}
void loop() {
//Read Raw ADC Data
int adcData = analogRead(sensorPin);
// Convert that ADC Data into voltage
float voltage = adcData * (5.0 / 1024.0);
// Convert the voltage into temperature
float temperature = voltage * 100;
// Print the temperature data
Serial.print(“Temperature: “);
Serial.print(temperature);
Serial.println(“*C”);
delay(800); // wait a second between readings
}

Working

Interfacing the LM35 temperature sensor with Arduino code is very simple and easy to understand. So, we need to read the analog data from the temperature sensor and convert it into temperature data. First, we need to initialize the code by describing the pin where the temperature sensor is connected. In the setup() function, we have to initialize the serial monitor just for debugging.

After that, in the loop function, we read the pin & store the ADC data within the ADC data variable. So the ADC data is converted to the voltage value & stored within the voltage. Lastly, we change the voltage to a temperature value, store it within a temperature variable, and print it on the serial monitor. Finally, we included 800ms & finished the code. Whenever we heat the temperature sensor through the hot air station, the temperature value will be increased, which will be noticed on the serial monitor.

Advantages & Disadvantages

The advantages of the LM35 sensor include the following.

• These are small, versatile, and simple-to-use temperature sensors.
• Its power consumption is low, approximately 60 µA,
• It is perfect for professional & educational projects that need consistent temperature measurements.
• It provides accurate temperature measurements with less calibration error.
• This sensor provides a linear output voltage.
• This sensor has a wide temperature range.

The disadvantages of the LM35 sensor include the following.

• It has limited temperature resolution.
• This module has a slow response time.
• It has a non-standard output voltage.
• These are susceptible to noise.
• These are not suitable for specialized applications that need specific features or abilities provided by other kinds of temperature sensors.

Applications

The applications of the LM35 sensor include the following.

• The LM35 sensor measures the temperature of a particular environment.
• You can use it as a temperature measurement device in HVAC applications.
• The LM35 sensor measures ambient temperature in both indoor and outdoor environments.
• Industries use these sensors for process control.
• Technicians monitor the HVAC system temperature with it to ensure proper functioning and identify potential issues.
• Engineers utilize these sensors for thermal security in automotive systems, such as monitoring engine temperature and preventing overheating.
• Researchers can also use it to measure and control temperatures in laboratory equipment and experiments.
• This sensor helps in monitoring and controlling temperatures within food processing applications.
• It helps in temperature monitoring & controlling within chemical-handling processes by ensuring security and avoiding accidents.
• This sensor provides thermal shutdown for an electronic component or circuit used within a particular project.
• This sensor measures battery temperature and provides battery protection against overheating.
• The LM35 sensor helps HVAC systems balance and adjust temperature controls by improving operational efficiency.

Please refer to this link for the LM35 sensor datasheet.

Thus, this is an overview of the LM35 sensor, its working, and its applications. This is a simple, accurate, and simple-to-use analog temperature sensor. It provides a linearly proportional o/p voltage to the temperature in Celsius, making it perfect for various applications. The benefits of this sensor are simple to interface, a linear output, low power consumption, etc. The application includes health monitoring, temperature monitoring, educational projects, etc. Here is a question for you: What is the LM34 sensor?