LM35

Interfacing LM35 Temperature Sensor with PIC Microcontroller.

The are many cool sensors available now a days, ranging from IR distance sensor modules, accelerometers, humidity sensors, temperature sensors and many many more(gas sensors, alcohol sensor, motion sensors, touch screens). Many of these are analog in nature. That means they give a voltage output that varies directly (and linearly) with the sensed quantity. For example in LM35 temperature sensor, the output voltage is 10mV per degree centigrade. That means if output is 300mV then the temperature is 30 degrees. In this tutorial we will learn how to interface LM35 temperature sensor with PIC18F4520 microcontroller and display its output on the LCD module.

First I recommend you to go and read the following tutorial as they are the base of this small project.

• Interfacing LCD Module with PIC Microcontrollers.
• Making the LCD Expansion Board for PIC18F4520.
• Using the ADC of PIC Microcontrollers.

After reading the ADC tutorial given above you will note the the PIC MCU’s ADC gives us the value between 0-1023 for input voltage of 0 to 5v provided it is configured exactly as in the above tutorial. So if the reading is 0 then input is 0v, if reading is 1023 then input is 5v. So in general form if the adc read out is valthen voltage is.

unsigned int val;

val=ADCRead(0); //Read Channel 0

voltage= ((val)/1023.0)*5;

The above formula give voltage in Volts, to get Voltage in mili Volts (mV) we must multiply it with 1000, so

voltage=((val)/1023.0)*5*1000); //Voltage is in mV

since 10mV = 1 degree, to get temperature we must divide it by 10, so

t=((val)/1023.0)*5*100); //t is in degree centigrade

simplifying further we get

t=((val/1023.0)*500);

t=(val*0.48876);

we round off this value, so

t=round(val*0.48876);

remember round() is a standard c library function