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Arduino - LM35 Temperature Sensor
Hardware Required
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About LM35 Temperature Sensor
Pinout
LM35 temperature sensor has three pins:
- GND pin: needs to be connected to GND (0V)
- VCC pin: needs to be connected to VCC (5V)
- OUT pin: signal pin gives the output voltage that is linearly proportional to the temperature, should be connected to a analog pin on Arduino.
How It Works
The LM35 outputs the voltage linearly proportional to the Centigrade temperature. The output scale factor of the LM35 is 10 mV/°C. It means that the temperature is calculated by dividing the voltage (mV) in output pin by 10.
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
How To Program For LM35 Temperature Sensor
- Get the ADC value from the temperature sensor by using analogRead() function.
int adcVal = analogRead(PIN_LM35);
- Convert the ADC value to voltage in millivolt
float milliVolt = adcVal * (ADC_VREF_mV / ADC_RESOLUTION);
- Convert the voltage to the temperature in Celsius
float tempC = milliVolt / 10;
- (Optional) Convert the Celsius to Fahrenheit
float tempF = tempC * 9 / 5 + 32;
Arduino Code
/*
* Created by ArduinoGetStarted.com
*
* This example code is in the public domain
*
* Tutorial page: https://arduinogetstarted.com/tutorials/arduino-lm35-temperature-sensor
*/
#define ADC_VREF_mV 5000.0 // in millivolt
#define ADC_RESOLUTION 1024.0
#define PIN_LM35 A0
void setup() {
Serial.begin(9600);
}
void loop() {
// get the ADC value from the temperature sensor
int adcVal = analogRead(PIN_LM35);
// convert the ADC value to voltage in millivolt
float milliVolt = adcVal * (ADC_VREF_mV / ADC_RESOLUTION);
// convert the voltage to the temperature in Celsius
float tempC = milliVolt / 10;
// convert the Celsius to Fahrenheit
float tempF = tempC * 9 / 5 + 32;
// print the temperature in the Serial Monitor:
Serial.print("Temperature: ");
Serial.print(tempC); // print the temperature in Celsius
Serial.print("°C");
Serial.print(" ~ "); // separator between Celsius and Fahrenheit
Serial.print(tempF); // print the temperature in Fahrenheit
Serial.println("°F");
delay(1000);
}
Quick Steps
- Copy the above code and open with Arduino IDE
- Click Upload button on Arduino IDE to upload code to Arduino
- Grasp the sensor by your hand
- See the result on Serial Monitor.
COM6
Temperature: 26.31°C ~ 79.36°F
Temperature: 26.44°C ~ 79.59°F
Temperature: 26.50°C ~ 79.70°F
Temperature: 26.56°C ~ 79.81°F
Temperature: 27.06°C ~ 80.71°F
Temperature: 27.75°C ~ 81.95°F
Temperature: 28.37°C ~ 83.07°F
Temperature: 29.00°C ~ 84.20°F
Temperature: 29.56°C ~ 85.21°F
Temperature: 30.00°C ~ 86.00°F
Temperature: 30.31°C ~ 86.56°F
Temperature: 30.62°C ~ 87.12°F
Temperature: 30.87°C ~ 87.57°F
Autoscroll
Clear output
9600 baud
Newline
Improving the Temperature Precision
In the above code, we use ADC reference voltage by default (5V~5000mV). We can increase the temperature resolution by changing reference voltage to INTERNAL (1.1V~1100mV). This reference voltage can be changed using the analogReference() function.
The below table show the diffrent between using 5000mV and 1100mV reference voltage
| Vref(mV) | 5000 mV (by default) | 1100 mV (INTERNAL) |
|---|---|---|
| Reading Resolution | 5000/1024 = 4.88 mV | 1100/1024 = 1.07 mV |
| Temperature Resolution | 0.488 °C | 0.107 °C |
| Temperature Range | 0 to 500 °C | 0 to 110 °C |
Arduino Code
/*
* Created by ArduinoGetStarted.com
*
* This example code is in the public domain
*
* Tutorial page: https://arduinogetstarted.com/tutorials/arduino-lm35-temperature-sensor
*/
#define ADC_VREF_mV 1100.0 // in millivolt
#define ADC_RESOLUTION 1024.0
#define PIN_LM35 A0
void setup() {
Serial.begin(9600);
// switch to Internal 1.1V Reference
analogReference(INTERNAL);
}
void loop() {
// get the ADC value from the temperature sensor
int adcVal = analogRead(PIN_LM35);
// convert the ADC value to voltage in millivolt
float milliVolt = adcVal * (ADC_VREF_mV / ADC_RESOLUTION); // ADC_VREF_mV = 1100 mV
// convert the voltage to the temperature in Celsius
float tempC = milliVolt / 10;
// convert the Celsius to Fahrenheit
float tempF = tempC * 9 / 5 + 32;
// print the temperature in the Serial Monitor:
Serial.print("Temperature: ");
Serial.print(tempC); // print the temperature in Celsius
Serial.print("°C");
Serial.print(" ~ "); // separator between Celsius and Fahrenheit
Serial.print(tempF); // print the temperature in Fahrenheit
Serial.println("°F");
delay(1000);
}
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