Measuring Room temperature using LM35 Temperature Sensor with Arduino

Measuring Temperature of a place through Arduino is very easy by using any of the commercial temperature sensor available in the market. I am going to measure the temperature using low cost and efficient lm35 analog output temperature sensor with arduino. For this tutorial we need an arduino board(Uno, Maga, Lenardo etc) and Lm35 temperature sensor. Lm35 is the oldest analog output temperature sensor still serving and available in the market. Some other old analog temperature sensors like TMP36 is also available in market but they are not popular among students, hobbyist and diy electronics project makers. I prepared a nice tutorial on Lm35 pin out its internal structure and working. I also derived temperature measuring formula for lm35 temperature sensor. I suggest you to take that tutorial if you are new and don’t know much about the lm35 temperature sensor. It will help you in understanding the code below.

Lm35 Pin out, working, temperature measuring formula and internal structure.

16x2 lcd displaying lm35 temperature value with arduino uno

16×2 lcd displaying lm35 temperature value with arduino uno

Lm35 Temperature sensor working

LM-35 Measuring room Temperature

Lm35 output voltage is proportional to centigrade/Celsius temperature. Lm35 Celsius/centigrade resolution is 10 mills volt. 10 mills volt represent one degree centigrade/Celsius. So if Lm35 outputs 100 mills volts the equivalent temperature in centigrade/Celsius will be 100/10 = 10 centigrade/Celsius. Lm35 can measure from -50 degree centigrade/Celsius up to 150 degree centigrade/Celsius.

Arduino analog pin is used to read the analog output signals from the sensor. The circuit diagram of the project is given below. To Pin#1 of Lm35 apply 5v, make Pin#2 ground, and the third one the middle pin is output pin. It gives a voltage signal that is actually the temperature of the particular place.

Note: LM35 is an absolute temperature sensor. It can only measure the temperature of the surroundings with in the circle of between 100 to 500 feet . So if you are using internet and you are matching your temperature reading from the one that is given for your city on a weather forecast site than your reading will not be same like theirs. It will be near but not the same.

Lm35 temperature sensor voltage to temperature conversion

Now one of the most difficult thing is how to convert the voltage generated/output by the lm35 sensor at output in Celsius or Fahrenheit scales. Well this needs you to first go through the data sheet of temperature sensor and know about the characteristics of the sensor.

Main crux from data sheet: LM35 Output temperature in Celsius form. It Increments the output by 1 on every 10 mV change in temperature.

when the sensor outputs 500 mv voltage, the temperature in Celsius is 50 degree Centigrade.
For 400 mv output temperature in Celsius is 40 degree centigrade.
For 600 mv temperature is 60 degree Celsius.

Now we now the resolution of Lm35 and its characteristics lets derive the formula to convert the output raw voltage by Lm35 in to centigrade/Celsius temperature.

Lm35 voltage conversion to temperature formula/equation derivation for Arduino

Arduino analog pins can measure up-to +5 volts OR the voltage on which it is working normally +5 volts.
Arduino analog pin resolution is 1023 starting from 0. On +5 volts input it counts to 1023.
Lm35 max voltage output is 1500mV( At 150 degree centigrade). 1500mV is equal to 1500/1000 = 1.5 volts. So Lm35 at max outputs 1.5 voltage.
Arduino analog pin count for 1.5 volts equals to (1.5 / 5)*1023 = 307.5 . At +5 volts its 1023 and at 1.5 volts its 307.5.
New Arduino-Lm35 Resolution = 307.5 / 150 = 2.048 . Now if arduino analog pin counts 2.048 its equal to 1 degree change in centigrade/Celsius temperature of LM35.

The same above formula/equation is in the code and its working perfectly.

LM35 with Arduino – Measuring Room Temperature

Arduino uno measuring temperature using Lm35 temperature sensor – Circuit diagram

The circuit diagram of the project is simple. Analog pin A0 of the arduino uno is used as input pin. Connect LM35 analog output pin to it. Apply +5 volts to Vcc pin of LM35 and ground the Gnd pin. In the loop function i am continuously measuring the temperature, and then i am printing the temperature on a 16×2 character lcd. I also converted the Celsius temperature in Fahrenheit with the formula that i think all of you are familiar with (temperature C ) * 9.0 / 5.0) + 32.0, then again i print the Temperature in Fahrenheit on 16×2 lcd. 16×2 lcd is interfaced in 4-bit mode with arduino. You can see the circuit diagram of the project below.

Note: For temperatures measurement i used the float data types to accurately measure the temperature in decimal form.

Lm35 temperature sensor 16x2 lcd with arduino uno - Measuring Temperature

Lm35 temperature sensor 16×2 lcd with arduino uno – Measuring Temperature

On first row of 16×2 lcd temperature in centigrade or Celsius scale is displayed and on second row of 16×2 lcd temperature in Fahrenheit scale is displayed. Temperature reading is updated after every 0.8 seconds.

More projects on interfaicning Lm35 temperature sensor with various other mirocontrollers. Each project code is open source. One can use and modify it according to his needs.

Lm35 With 89c51 Microcontroller Measuring Temperature

Lm35 WiFi temperature monitoring using Nodemcu

Measuring Room Temperature with Arduino Code

Watch the Project Video Here!!!!
Sorry for the bad quality of the video