Digital Thermometer with Arduino Uno

Below, is my effort to design a digital thermometer using the Arduino Uno. My attempt was a continuous research in the internet, googling every time my questions that born in my mind. All the code is copying and pasting from other users attempts, with big or small changes from me, but adapted to fit to my project.

There is a lot of fun out there with the microcontrollers. You can control every electronic device from one thermometer to a big project of a chemical process. The field is huge, but I want to share only a foo sand with yours.

The project is consists of three parts or steps:

• Design the circuit in Fritzing IDE and then making it in a real breadboard.
• Write a code in Arduino IDE in order to make the microcontroller to work properly with serial communication port of my PC. Also the Arduino IDE help the user to download the program into chip microcontroller enable it to work alone until a new program insert to it.
• Write a code in Processing IDE to make a usefriendly window interface. This allows to monitoring the measured values and saves data in real time. All the programs are free to download, accompanied by many examples. With a little google help it is easy to understand and how to make your "homemade" code. All the code is based on the processing language with smal changes for arduino software.

Of course you can use one software for all, but this is another issue.

The circuit is using as temperature sensor, a thermistor of 10k with a resistor of 10k in series, making a voltage devider like below (my preference voltage operation is 5.0 volt):

Voltage Divider connected with arduino microcontroller pins

Below is the breadboard schematic of the circuit, which is designed in Fritzing software. The file is free to download.

Breadboard circuit of digital thermometer

The mathematical model which is used to determine the temperature, is the Steinhart-Hart Thermistor Equation:

where:

• a, b and c are called the Steinhart-Hart parameters, and must be specified for each device. 
• T is the temperature in kelvin and 
• R is the thermistor resistance in ohms. 

The error in the Steinhart-Hart equation is generally less than 0.02 °C in the measurement of temperature over a 200 °C range. As an example, typical values for a thermistor with a resistance of 3000 Ω at room temperature (25 °C = 298.15 K) are:

The constants for a thermistor 10.000 ohms, that I use in my circuit, are:

α = 0.001129148

b = 0.000234125 

c = 8.76741E-08

The results are screening in a mobile LCD screen. The screen belongs to the Nokia 5110 and it is compatible with 3310 LCD, because they have the same controller (PCD8544 ). It functions in 2.7 to 3.3 volt, has 48x84 pixel matrix and 8 connection pins.

Nokia LCD 5110 (Familly of PCD8544 controller)

In order to make the LCD screen working properly you have to download the corresponding library and connect the LCD pins with the Arduino Uno pins, like below:

LCD Nokia 5110 and 3310 connection information 

The measured values are being monitoring by the user with a user friendly program. Also the measured values are screening in the LCD while you can save the data in EXCEL file every time the sensor is measuring the temperature

Arduino Program
Below is the code written in Arduino IDE. Copy and paste it in the Arduino software.

All the code is free to download.

The heart of the code is below:

float temp;
float tempDEC;
for (int i=0; i<=7; i++){
samples[i] = Thermistor(analogRead(ThermistorPIN));
temp = temp + samples[i];
}
temp = temp/8.0;
Serial.println(temp,DEC);

The microcontroller takes first, 8 samples and then compute the average value (temp = temp/8.0;). After that procedure, the Arduino send the signal in PC through serial communication port of my PC, with full decimal precision ( Serial.println(temp,DEC); ).

Processing Program (Userfriendly Interface)

Below is the code written in processing language and the screenshot of the program. I tried to write a lot of comments inside the code in order to understand someone what is the "mechanism" behind each line and what you expect to get if you make changes. The experiment is the begining to answer your questions.

Digital Thermometer monitoring program

Below you can see the video that describes the monitoring program:

You can copy and paste the code for the monitoring program in the Processing IDE, here.

The data are saving in EXCEL file within 3 columns. The 1st column records the date, the 2nd the time and 3rd the temperature value with 2 decimals. The name of the file includes all the date information and it's a unique every time runing the program.

The filename form is:

data_ddmmyyyy-hhmmss.xls

The file is saving in the folder name "datalogger", which is created the first time you runing the interface. Also, I wrote a macro excel command which creates the graph in automated way. The macro is free to download. Insert the code in the module of "personal.xls" file in able to run the macro every time you want. Below is the macro with instructions where to put:

At the begining of my journey, my little knowledge about the microcontrollers it leads me to more and more questions, for small and big issues. My reasearch leads me to add and write code to overcome the new problems optimizing my project. However my knowledge remains in minimum level until now. I hope to help someone who is in the begining, like me.

Have a nice fun !!