Friday, October 17, 2014

Temperature Sensor For Development Board

Welcome back and good day everyone.

This will be a small post about a temperature sensor that can be used with development boards like Arduino, Raspberry Pi or similar products. This circuit is a very simple and easy to make circuit. This circuit is based on a precision integrated circuit that has an output voltage linearly proportional to temperature. So higher the voltage is higher the temperature is. We can simply read the output voltage and convert it to centigrade temperature scale.


+2 Degree To +150 Degree Centigrade

-55 Degree To +150 Degree Centigrade

How It Works?

LM35 looks like a small TO-92 package transistor but it actually is an integrated circuit. This integrated circuit is from Texas Instrument. This IC can be operated from 4V to 30V, that means you can't run it on 3.3V but 5V will be fine for it.

If you check the datasheet of the IC you will see that it's output is Linear + 10mV/Degree Centigrade that means 10mV represents 1 degree Centigrade. So 0.25V will represent 25 Degree Centigrade. Although this IC can read from -55Degree to +150 degree, you will need slightly different diagram for that and also you will need dual polarity power supply for that. For the value of resistance use the theorem to calculate the value.

From the circuit diagram it can be seen that it is powered from a 5V source, a capacitor is used to slightly stabilize the output. You can use a lower valued one or higher valued one if you want(even a 100uF electrolytic will be fine). This circuit can easily be built on a small PCB. 

How to Interpret

While converting A to D ( Analog to Digital ) all you need to do is to use the fact that 10mV stands for 1 degree centigrade, Measuring the voltage you will get the actual temperature. 

More Information

1. LM35 Datasheet.
2. Dual Polarity Power Supply.
3. My other posts

Happy Experimenting.

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