Mechanism for measuring atmospheric temperature

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LM35 temperature sensor

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Analog to digital conversion functionality of
the microchip

**LM35 Precision Centigrade Temperature Sensor**

LM35 series produced by National Semiconductors is a
precision integrated circuit temperature sensor series which are designed to
produce an output voltage that is linearly proportional to the Celsius
temperature. The output voltage is 10mV per degree Centigrade.

Advantages/ Features

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Calibrated directly in Celsius

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Linear 10mV/`C scale factor

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Can operate in the range of -55`C – 150`C

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0.5`C accuracy guaranteeble (@25`C)

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Less than 60µA current drain

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Operates from 4V to 35V

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Low self-heating (0.08`C in still air)

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Low impedance output (0.1Ω per 1mA load)

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Low cost

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Easily available

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Suitable for remote applications (low power
consumption)

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The sensor is commonly used for such application

**Calculations**

Assume the ADC of the PIC gives the values between 0 to n
for input voltage of 0 to 5v provided. (eg: if the reading is 0 then input is
0V, if the reading is n the input is 5V). The PICs we are planning to use,
PIC16F877a or PIC18 series, have a 10 bit ADC. Thus the max value for the 10
bit ADC will be 1023)

N = 1023

If the value read from the ADC = α

Voltage = (α/n)*5

Voltage in mV = (α/n)*5*1000

Since 10mV = 1`C

Temperature = (α/n)*5*100 = (α/n)*500

Substituting n = 1023

Temperature = (α/1023)*500 = α * 0.48876 `C

We can use this equation to directly calculate the instantaneous
temperature of the atmosphere.

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