Digital Thermometer Reloaded

8/3/2019 Digital Thermometer Reloaded

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AMBIENTTEMPERATUREDIGITAL MONITOR

By:

PIYUSH - 2K10\EC\097


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CERTIFICATE

This is to certify thatName - PIYUSHBranch - Electronics and CommunicationRoll no 2k10\EC\097has successfully completed the digital electronics project on Ambient Temperature Digital Monitor.

Teachersignature

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ABSTRACT

This project intends to display the ambient room

temperature as measured by the LM-35(temperature sensor) which is directly calibrated indegree Celsius. The analog output from thetransistor is fed into the micro-controller through

ADC programming. The final temperature isdisplayed in lcd.

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INTRODUCTION

This digital thermometer can measure temperatures up to 150C withan accuracy of 1C. The transistor used this way makes a low-costsensor. Theentire circuit works off a 9V battery.

These sensors use a solid-state technique to determine thetemperature. That is to say, they dont use mercury (like old

thermometers), bimetalic strips(like in some home thermometers orstoves), nor do they use thermistors (temperature sensitive resistors).Instead, they use the fact as temperature increases, the votage acrossa diode increases at a known rate. (Technically, this is actually thevoltage drop between the base and emitter - the Vbe - of a transistor.LM-35 is calibrated directly in Celsius (Centigrade).

Because these sensors have no moving parts, they are precise, neverwear out, don't need calibration, work under many environmentalconditions, and are consistant between sensors and readings.

The analog readings of LM-35 are converted into its digital counterpartthrough microcontroller (A and the resultant output is shown throughlcd interfacing.

The lcd shows one temperature measurement is taken about everysecond and displayed as current temperature. Every 8 measurementsa temperature average of those is calculated and displayed as Av.T.The same time a calculation about the min, max average temperatureis done ( displayed as Min and Max) for all the power on one period ofArduino board.

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http://en.wikipedia.org/wiki/Bimetallic_striphttp://en.wikipedia.org/wiki/Thermistorhttp://en.wikipedia.org/wiki/Bimetallic_striphttp://en.wikipedia.org/wiki/Thermistor


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CONTENT

CIRCUIT DIAGRAM

PRELIMINARY ANALYSIS

TEMPERATURE SENSOR-LM35

LM35 STRUCTURE

MICROCONTROLLER ARDUINO

ARDUINO

READING THE ANALOG TEMPERATURE DATA

PROGRAMMING

LCD INTERFACING

CONCLUSION

BIBLOGRAPHY

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CIRCUIT

Fig: Showing the Arduino Board with LCD interfacing

Parts:

1. Arduino Board

2. LCD 2x16 screen3. 10k Potentometer

4. Breadboard

5. LM-35 transistor 6. Connecting wires

7. Resistors and Capacitors.

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SCHEMATIC DIAGRAM

Calibration of the digital thermomet

To set the minimum level (00C), place the diode in a glass of water filled with crushed ice (check thetemperature first with a normal thermometer) wait until the thermometer shows zero degrees centigra

P1 so that the digital voltmeter will display 000 when the diode senses zero degree centigade.

To set the maximum level (1000C), place the diode sensor into a boiling water and adjust P2 so that t

digital meter exactly displays 99.9.

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PRELIMINARY ANALYSIS

Testing these sensors requires a battery pack or power supply.

Connect a 2.7-5.5V power supply so that ground is connected to pin 3

(right pin), and power is connected to pin 1 (left pin)

Then connect your multimeter in DC voltage mode to ground and the

remaining pin 2 (middle). The voltage across LM-35 transistor will be0.25V.

FIG:- The sensor is indicating that the temperature is 26.3C

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http://www.ladyada.net/images/sensors/tmp36test.jpg


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How to measure temperature!

We simply connect the left pin to power (2.7-5.5V) and the right pin to ground. Then the middle pin

will have an analog voltage that is directly proportional (linear) to the temperature. The analog voltage

is independant of the power supply.

To convert the voltage to temperature, we simply use the basic formula:

Temp in C = [(Vout in mV) - 500] / 10

So for example, if the voltage out is 1V that means that the temperature is ((1000 mV - 500) / 10) = 50

C

ON using a LM35, use line 'a' in the image above and the formula: Temp in C = (Vout in mV) / 10

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TEMPERATURESENSOR

LM-35

Features

Calibrated directly in Celsius (Centigrade) Linear + 10.0 mV/C scale factor

0.5C accuracy guaranteeable (at +25C) Rated for full -55 to +150C range Suitable for remote applications

Low cost due to wafer-level trimming Operates from 4 to 30 volts

Less than 60 A current drain

Low self-heating, 0.08C in still air Nonlinearity only C typical

Low impedance output, 0.1 Ohm for 1 mA load

Description

The LM35 series are precision integrated-circuit temperature sensors,whose output voltage is linearly proportional to the Celsius

(Centigrade) temperature. The LM35 thus has an advantage over

linear temperature sensors calibrated in Kelvin, as the user is notrequired to subtract a large constant voltage from its output to obtain

convenient Centigrade scaling. The LM35 does not require any externalcalibration or trimming to provide typical accuracies of C at room

temperature and C over a full -55 to +150C temperature range.Low cost is assured by trimming and calibration at the wafer level. The

LM35's low output impedance, linear output, and precise inherent

calibration make interfacing to readout or control circuitry especiallyeasy. It can be used with single power supplies, or with plus and

minus supplies. As it draws only 60 A from its supply, it has very low

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self-heating, less than 0.1C in still air. The LM35 is rated to operate

over a -55 to +150C temperature range.

LM-35 STRUCTURE

The figure showing the two temperature controlled resistors that

control the temperature sensing capability of LM-35.

Schematic diagram showing LM-35 with the three output terminals along with theirworking.

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MICROCONTROLLER

ARDUINO

Microcontroller board

Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use

hardware and software. Arduino can sense the environment by receiving input from a

variety of sensors and can affect its surroundings by controlling lights, motors, and other

actuators. The microcontroller on the board is programmed using theArduino

programming language and the Arduino development environment.

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http://arduino.cc/en/Reference/HomePagehttp://arduino.cc/en/Reference/HomePagehttp://arduino.cc/en/Reference/HomePagehttp://arduino.cc/en/Reference/HomePage


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ARDUINO

Arduino is anopen-sourcesingle-board microcontroller, descendant of the open-source

Wiring platformdesigned to make the process of using electronics in multidisciplinaryprojects more accessible. The hardware consists of a simple open hardware design for the

Arduino board with anAtmel AVRprocessor and on-boardI/O support. The software

consists of a standard programming language compiler and theboot loaderthat runs on

the board.

Arduino hardware is programmed using a Wiring-based language (syntax + libraries),

similar to C++with some simplifications and modifications, and a Processing-basedIDE.

(Integrated development environment)

Currently shipping versions can be purchased pre-assembled; hardware design

information is available for those who would like to assemble an Arduino by hand.Additionally, variations of the Italian-made Arduinowith varying levels of

compatibilityhave been released by third parties; some of them are programmed using

the Arduino software.

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http://en.wikipedia.org/wiki/Open-source_hardwarehttp://en.wikipedia.org/wiki/Open-source_hardwarehttp://en.wikipedia.org/wiki/Single-board_microcontrollerhttp://en.wikipedia.org/wiki/Wiring_(development_platform)http://en.wikipedia.org/wiki/Wiring_(development_platform)http://en.wikipedia.org/wiki/Atmel_AVRhttp://en.wikipedia.org/wiki/Atmel_AVRhttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Booting#Boot_loaderhttp://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/Processing_(programming_language)http://en.wikipedia.org/wiki/Integrated_development_environmenthttp://en.wikipedia.org/wiki/Integrated_development_environmenthttp://en.wikipedia.org/wiki/Integrated_development_environmenthttp://upload.wikimedia.org/wikipedia/commons/4/42/Arduino_Uno_logo.pnghttp://upload.wikimedia.org/wikipedia/commons/a/a7/Arduino_IDE_-_v0011_Alpha.pnghttp://en.wikipedia.org/wiki/Open-source_hardwarehttp://en.wikipedia.org/wiki/Single-board_microcontrollerhttp://en.wikipedia.org/wiki/Wiring_(development_platform)http://en.wikipedia.org/wiki/Atmel_AVRhttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Booting#Boot_loaderhttp://en.wikipedia.org/wiki/C%2B%2Bhttp://en.wikipedia.org/wiki/Processing_(programming_language)http://en.wikipedia.org/wiki/Integrated_development_environmenthttp://en.wikipedia.org/wiki/Integrated_development_environment


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READING THE ANALOGTEMPERATURE DATA

We can use anywhere between 2.7V and 5.5V as the power supply. Wecan use a 5V supply but note that we can also use this with a 3.3v

supply just as easily. No matter what supply we use, the analog

voltage reading will range from about 0V (ground) to about 1.75V.

On using a 5V Arduino, and connecting the sensor directly into anAnalog pin, we can use these formulas to turn the 10-bit analog

reading into a temperature:

Voltage at pin in millivolts = (reading from ADC) *

(5000/1024)

This formula converts the number 0-1023 from the ADC into 0-5000mV (= 5V)

If using a 3.3V Arduino, we want to use this:

Voltage at pin in millivolts = (reading from ADC) *(3300/1024)

This formula converts the number 0-1023 from the ADC into 0-3300mV (= 3.3V)

Then, to convert millivolts into temperature, use this formula:

Centigrade temperature = [(analog voltage in mV) - 500] / 10

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PROGRAMMING

// Arduino LCD Ambient Temperature Monitor.

// Displays Current, 8 sec Average, Max and Min Temperature.

// To wire your LED screen to your Arduino, connect the following pins:

// LCD RS pin to digital pin 12

// LCD Enable pin to digital pin 11// LCD D4 pin to digital pin 5

// LCD D5 pin to digital pin 4// LCD D6 pin to digital pin 3

// LCD D7 pin to digital pin 2// additionally, wire a 10K pot to +5V and GND, with it's wiper(output) to LCD screens VO pin (pin3).

// We used the on board power source (5v and Gnd) to power theLM35 and analog pin 0 (zero) to read the analog output from the

sensor.

// 3 NOVEMBER 2011

// include the library code:

#include // include the LCD driver library

//declare variables

float tempC = 0; // variable for holding Celcius temp (floating fordecimal points precision)

float tempf = 0; // variable for holding Fareghneit temp

int tempPin = 0; // Declaring the Analog input to be 0 (A0) of Arduinoboard.

float samples[8]; // array to hold 8 samples for Average tempcalculation

float maxi = 0,mini = 100; // max/min temperature variables withinitial values. LM35 in simple setup only measures Temp above 0.

int i;

// initialize the library with the numbers of the interface pins

LiquidCrystal lcd( 7, 8, 9, 10, 11, 12);void setup()

{

Serial.begin(9600); //opens serial port, sets data rate to 9600 bps

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pinMode(13, OUTPUT); // The Red arduino led

lcd.begin(16, 2); // set up the LCD's number of columns and rows:

lcd.setCursor(0, 0);lcd.print("LCD Ambient Temp");

lcd.setCursor(0, 1);lcd.print(" Digital Monitor ");delay(5000);

lcd.clear();lcd.setCursor(0, 0);

lcd.print("All temp are in "); // print text to LCD

lcd.setCursor(0, 1);lcd.print("degree celsius");

delay(5000);lcd.clear(); // clear LCD display

}

void loop()

{digitalWrite(13, LOW); // set the LED on

Serial.println(analogRead(tempPin)); // Displays on serial monitor thesampled value before conversion to real Temperature reading

// Start of calculations FOR loop.for(i = 0;i


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Serial.println(""); // Like and CR at serial monitor

Serial.println("");

tempC = tempC/8.0; // calculated the average of 8 samples in Celsius

tempf = (tempC * 9)/ 5 + 32; // converts to Fahrenheit

if(tempC > maxi) {maxi = tempC;} // set max temperatureif(tempC < mini) {mini = tempC;} // set min temperature

// Send Results to Serial MonitorSerial.println("New measurement");

Serial.print(" Average Temperature in Celcius is " ); //send thedata to the computer

Serial.println(tempC);//send the data to the computerSerial.print(" Average Temperature in Farenait is " ); //send

the data to the computer

Serial.println(tempf);//send the data to the computerSerial.print(" MAX Temperature in Celcius is " ); //send the

data to the computerSerial.println(maxi);//send the data to the computer

Serial.print(" MIN Temperature in Celcius is " ); //send the

data to the computerSerial.println(mini);//send the data to the computer

// Send results to LCD.

lcd.setCursor(0, 0);lcd.print("Av.T Max Min");

// set the cursor to column 0, line 1// (note: line 1 is the second row, since counting begins with 0):

lcd.setCursor(0, 1);// print the measured temp average

lcd.print(tempC);

lcd.setCursor(6, 1);// print the maximum temp

lcd.print(maxi);

lcd.setCursor(12, 1);// print the minimum templcd.print(mini);

digitalWrite(13, HIGH); // set the LED off

delay(3000); // Wait about 3 seconds to display the results to LCDscreen befor starting the loop again

tempC = 0; // Set tempC to 0 so calculations can be done again

}

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LCD INTERFACING

The Displaytech 162B is a HD44780 compatible device, and interfacethem with the Arduino. They can be driven with a eight data lines -

which uses up most of the digital I/O pins on the Arduino, or more

sensibly you can use 4 bit mode.

LCD Pin Connected to

1 Backlight Anode +5V (via small resistor)

2 Backlight Cathode GND3 Ground GND

4 Supply V for Logic +5V

5 Input Voltage for LCD Middle pin of 50K potentiometer6 RS (Data/Instruction) Ard pin 12

7 R/W (Read/Write) GND8 E (Enable) Ard pin 2

9 Data bit 0

10 Data bit 111 Data bit 2

12 Data bit 313 Data bit 4 Ard pin 7

14 Data bit 5 Ard pin 8

15 Data bit 6 Ard pin 916 Data bit 7 Ard pin 10

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The other two pins of the potentiometer are connected to +5V andGND and provide a contrast control (and we will need it at least

initally). 50K is over the top for the purpose, 10K is more typical.The resistor on the backlight was added because the backlight LED on

the board was getting rather warm. The display stays bright enoughand runs a bit cooler with a resistor on the supply.The pin allocations on the Arduino were dictated by the LCD4Bit

library.Twist the potentiometer to get a readable display.

Following pin diagram corresponds us to make the necessary changes in the program.

LCD pin name RS EN DB4 DB5 DB6 DB7

Arduino pin # 7 8 9 10 11 12

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

And change it to:

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

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CONCLUSION

The lcd shows one temperature measurement which is taken aboutevery second and displayed as current temperature. Every 8measurements a temperature average of those is calculated anddisplayed as Av.T. The same time a calculation about the min, maxaverage temperature is done ( displayed as Min and Max) for all thepower on one period of Arduino board.

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BIBLOGRAPHY

The idea for the following project has been taken from:-

http://www.ladyada.net/learn/lcd/charlcd.html

http://www.national.com/mpf/LM/LM35.html#Overview

http://www.ladyada.net/learn/sensors/tmp36.html

Electronics for You 2010
http://www.ladyada.net/learn/lcd/charlcd.htmlhttp://www.national.com/mpf/LM/LM35.html#Overviewhttp://www.ladyada.net/learn/sensors/tmp36.htmlhttp://www.ladyada.net/learn/lcd/charlcd.htmlhttp://www.national.com/mpf/LM/LM35.html#Overviewhttp://www.ladyada.net/learn/sensors/tmp36.html

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Digital Thermometer Reloaded