Previous post describes what a temperature sensor is & about how to test the well known & well available analog temperature sensor in the market, the LM35 temperature sensor.
This article will describe how to interface LM35 with Arduino, a well known open-source development platform. There are many versions of Arduino available in the market. We are using Arduino UNO board here. It contains a micro-controller ATMEGA328, the brain of the platform, six numbers of Analog input pins, 14 numbers of digital pins out of them 6 numbers of pins are PWM ~ (Pulse Width Modulation) pins.
LM35 has three pins, pin no.1 is +Vcc, pin no.2 is Output & pin no.3 is Ground. As it is a analog temperature sensor so the output pin of the LM35 will be connected to the Analog Input pin of Arduino. Other pins to the 5V & GND pin.
The hardware part is done.
Coding part of this is simple. We will use the Serial Monitor to visualize the response of LM35. Later interfacing another display like LCD or 7 segment LED with the arduino we can also make this project more compact.
- float temp : “temp” is a float variable
- int tempPin = 0 : declaration for the Analog Input pin(A0)
- Serial.begin(9600) : declaration for the Baud Rate of the serial port which is 9600.
- temp = analogRead(tempPin) : the function analogRead is to read analog data from the tempPin
- Serial.print() : To print something in the serial port
- temp = temp * 0.48828125
0.48828125 where this number came from??
This is (+Vcc * 1000 / 1024) / 10
Where +Vcc is the supply voltage = +5V, 1024 is 2^10, value where the analog value can be represented by ATmega the actual voltage obtained by VOLTAGE_GET / 1024.
1000 is used to change the unit from V to mV & 10 is a constant as each 10 mV is directly proportional to 1 Celsius in LM35.
So (5.0 * 1000 / 1024) / 10 = 0.48828125.
Now connect the Arduino to the PC, open the arduino software and upload the code to the arduino. Now press Ctrl + Shift + M, this will open the serial monitor & you can see your room temperature. Done!
Written by : Subhadeep Biswas