CODEWITHSUNDEEP
arduinosensors
shajib0o
shajib0o

Reputation: 621

what is conversion system of LM35 (temperature sensor) in Celsius?

I see formula like 

temp = (5*val*100/1024)

Can anyone tell me the details of this formula?

Upvotes: 3

Views: 36842

Answers (2)

Trustchidi
Trustchidi

Reputation: 11

for Arduinos;

val = analogRead(tempPin);

float mv = ( val/1024.0)*5000; 

float cel = mv/10;

Upvotes: 1

zmo
zmo

Reputation: 24802

the truth always lies within the datasheets:

The Atmega ADC: Analog to Digital Converter

Your Atmega is powered by 5V, and the datasheet of the Atmega states that its ADC has a definition of 1024 values (i.e. 10bits). So in your formula, 5/1024 is representing each voltage step represented by a bit:

0.0000V -> 0b0000000000
0.0048V -> 0b0000000001
...
5.0000V -> 0b1000000000

Getting value out of the LM35

If you read the application notes in the LM35 datasheet, you'll find the following formula:

Vout=10mV/°C

if you're binding the LM35 with a 200ohms resistor. So if you use the rule of three, you'll get:

Vout=0.01/°C
°C=Vout/0.01
°C=Vout/0.01
°C=Vout*100

HTH

Upvotes: 6

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