LM 35 TEMPERATURE SENSOR The LM 35 is

LM 35 TEMPERATURE SENSOR The LM 35 is an integrated circuit sensor that can be used to measure temperature with an electrical output proportional to the temperature (in o. C)

PIN OUT OF LM 35

WHY LM 35 ? ? You can measure temperature more accurately than a using a thermistor. The sensor circuitry is sealed and not subject to oxidation, etc. The LM 35 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 =5 V There are 1024 steps between 0 and +5 volts .

INTERNAL CIRCUIT OF LM 35

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 R 1 that is proportional to the absolute temperature

Contd… The amplifier at the top ensures that the voltage at the base of the left transistor (Q 1) 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 (LM 34 or LM 35)

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

contd val = analog. Read(temp. Pin); float mv = ( val/1024. 0)*5000; float cel = mv/10; float farh = (cel*9)/5 + 32;

Contd… Serial. print("TEMPRATURE = "); Serial. print(cel); Serial. print("*C"); 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 DHT 11 - moisture and humidity sensor Thermistor 10 k – body temperature