LM35 TEMPERATURE SENSOR  The LM35 is an integrated circuit sensor that can be used to measure temperature with an electrical output proportional to the temperature (in oC)

PIN OUT OF LM35

WHY LM35 ?? You can measure temperature more accurately than a using a thermistor. The sensor circuitry is sealed and not subject to oxidation, etc. The LM35 generates a higher output voltage than thermocouples and may not require that the output voltage be amplified.

BASIC FORMULA Vout = analog input voltage/step size Vref =5V There are 1024 steps between 0 and +5 volts .

INTERNAL CIRCUIT OF LM35

WORKING  There are two transistors in the center of the drawing. One has ten times the emitter area of the other. one tenth of the current density This causes a voltage across the resistor R1 that is proportional to the absolute temperature

Contd… The amplifier at the top ensures that the voltage at the base of the left transistor (Q1) is proportional to absolute temperature (PTAT) by comparing the output of the two transistors The amplifer at the right converts absolute temperature (measured in Kelvin) into either Fahrenheit or Celsius, depending on the part (LM34 or LM35)

CODE int val; int tempPin = 1; void setup() {   Serial.begin(9600); } void loop() {  

contd val = analogRead(tempPin); float mv = ( val/1024.0)*5000;   float cel = mv/10;   float farh = (cel*9)/5 + 32;

Contd… Serial.print("TEMPRATURE = "); Serial.print(cel);   Serial.println();   delay(1000);

Contd.. /*  uncomment this to get temperature in farenhite    Serial.print("TEMPRATURE = ");   Serial.print(farh);   Serial.print("*F");   Serial.println();

Some other temperature sensors DHT11- moisture and humidity sensor Thermistor 10k – body temperature