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This project refers to an Arduino sketch which uses an ultrasonic sensor for calculating the time return of the ultrasonic signal emitted by the sensor and the object reflecting the signal back. Then, with the help of appropriate physicomathematical formulas, it performs calculation of the distance between the sensor and the object causing the reflection signal. Also, the system includes a piezo speaker used to produce a tune when an object is detected too close nearby. This system could be used in security doors, on cars as a helper to park or anywhere else where distance at close proximity is important.

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This project refers to an Arduino sketch which uses an LCD display (as output device) with in-built elementary Keypad (as input device) to display information from sensors. In this project, there are temperature, light and motion sensors. If we want to check the value of one of the sensors, we can do it via the keypad onto the LCD screen. We can choose the sensor of interest using the keys UP and DOWN.

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This project refers to an Arduino sketch that implements a true random number generator with the help of an audio sensor. The sensor measures the sound volume in the nearby environment. The Arduino acts as a network device with an appropriate WEB interface in it from which we can access the random numbers. This technology is not new as it exists in other network devices. For example, routers or network printers have a WEB interface.

The WEB interface is installed in the Arduino itself and is supported with the help of a simple but quite progressive web server (which is also located within the Arduino). The Arduino is connected to the Internet with a special Ethernet card (Ethernet Shield). The Ethernet card is assigned with a static IP (because the Arduino in this case does not work as a client but as a server since the web server is executed there at port 80).

To enable the sound sensor to collect really random values as regards the volume of sound in the environment, it helps to place it in a noisy room or near a radio.

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This project refers to an Arduino sketch which with the help of a relay (electromechanical switch) and the VRBot system can drive an external device (eg. a household lamp, a car alarm, a home air conditioner etc.) with voice commands. The system VRBot is properly trained with voice messages and then performs voice recognition.

More specifically, the Arduino detects acoustic sounds and tries to recognize them through the system VRBot. Finally, if acceptable voice messages are identified, the Arduino manages them for the use of the device driven with the help of the relay.

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This project refers to an Arduino sketch that implements an online Morse Code web encoder. The Morse Code is until now a global communication system. However, it is now rarely used (it has been previously extensively used in the Navy and the Army in general). In this project, the Arduino works as a server, which remote clients can be connected to with the help of TCP sockets and send occasional messages on a regular alphanumeric form.

For example: “SOS! USA NAVY (12/02/1920, 23:00)”

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The presence of errors in software development (and not only) is inevitable. However, over time the programs improve and tend to perfection through various techniques and methods we have developed.

The deterministic problems are easy to spot because they always lead to the same error. There are tools that run through the source code of an application to find possible deterministic errors (these tools are especially useful in applications written with scripting languages such as Python, Bash Scripting, etc).

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This project refers to an Arduino sketch that implements a motion detector using a passive infrared sensor (PIR), a piezo speaker, two switches for functions such as ON, OFF and an LED as function indicator. When the detector is in OFF state then it performs no real function (just turns off the function indicator), and when in ON state, then the program turns on the function indicator and checks whether there is motion (the detection range of the detector is about 6 feet) in the area (via the sensor PIR) to produce a tune with piezo speaker. This process is repeated continuously as long as there is movement and until the switch OFF is pressed.

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Below I quote a function in C to convert a standard Linux kernel process into background service (Daemon Service). If you wish to develop a server to provide services, it may be helpful. Although there are several manuals on the Internet on how to create background services, most of them don’t show a complete example, while others are barely functioning. The following function converts a standard process into a service taking everything you need into account. Also, this function is the result of a combination of several textbooks and numerous studies about this issue. Finally, it has been tested on personal applications servers and it is performing well.

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Below I quote a simple implementation in C that you can use in your applications for the management of software signals in POSIX operating systems (such as the GNU/Linux). Of course, this implementation comes from a personal project of the past, especially where I grappled with system programming. You can modify this implementation to work best with your needs.

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Before I mention the function that I have developed for the production of random numbers from the monolithic Linux kernel, I would first like to say something about the issue of random numbers.

The issue of producing truly random numbers is important and had even since the beginning puzzled computer scientists. In mathematics, it is very difficult to define the random and, generally, randomness is very difficult to prove with no assumptions. In the past, many scientists tried to develop mathematical models and algorithms to develop random number generators.

One of the greatest scientists of Computer Science, John von Neumann (the basic idea of the architecture of all computer systems today was his own design) jokingly said: ‘Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.’.

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Below I quote a program in C which performs memory test in a computer system (for example the BIOS performs a memory test before loading the operating system loader in any IBM PC). However, what we quote is different in its implementation. If you are dealing with embedded systems or operating systems programming it may be useful.

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The QT provides an adorable way to store the settings of a program with a GUI (and not only) by means of the QSettings library. Below, we quote a personal version of the project ‘parkman‘ (Parking Manager).

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Below I quote a simple but useful library (implemented in C++) which contains functions for comparing double precision floating point numbers.

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This project refers to an Arduino sketch which allows the rotation of three dimensional shapes using appropriate sensors. Essentially, the Arduino collects values from the sensors and corresponds them to the [0, 360] range (rotation angle). Every time we get a pair of values (X, Y) for the rotation of the shape, the pair is sent over the USB serial port to the PC.

The PC runs a Python script which produces three-dimensional shapes with OpenGL. Also, the script obtains the pairs via the USB serial port and renews the current shape of the screen. For performance reasons, the three-dimensional shape is renewed only when there are changes in the pair (X, Y).

Finally, you should know that to run the Python script properly the Arduino should already be running and input sensors should have been calibrated regarding their edges. The calibration is performed automatically in the first 15 seconds (use two potentiometers as an example for both input sensors).

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This project refers to an Arduino sketch which implements a POV (Persistence Of Vision) case for the representation of text messages which can contain the visible characters of the character set ASCII.

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This project refers to an Arduino sketch that implements a light indicator with the help of an external sensor (photoresistor) for the recognition of light (the sensor acts as input device for the Arduino), and a bar graph of many LEDs used as a rating indicator (the indicator functions as an output device for the Arduino).

In this project we use an 8-bit shift register (namely the 74HC595). This way we can drive 8 different LEDs in the output committing only three PINS of the Arduino.

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The Ben 10 cube presented enough interest. Although it is like the classic Rubik’s cube, it had some peculiarities.

Specifically, in order to solve it you need to concentrate your attention on the central square of each side so you can always orient it accordingly in the right direction to finalize plans without irregularities.

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Within the framework of the course “Programming II – Laboratory” (Department of Informatics and Communications, T.E.I. of Central Macedonia) we were asked to implement as homework a program that reads characters from the standard input and then export to standard output a frequency histogram of the characters that appear.

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This project refers to an Arduino sketch which with the help of an external temperature sensor (input device) can control the rotation speed of a DC motor (output device). Also, during the execution of the program, there is dynamic calibration as regards the input values of the temperature sensor.

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This project refers to an Arduino sketch which is used to produce LEDs animations. So, we use an 8-bit shift register (namely the 74HC595). This way we can drive 8 different LEDs in the output committing only three PINS of the Arduino.

If we want to drive more LEDs, we connect into a cascade form two or more (depending on the number of LEDs we want to support) shift registers and act accordingly.

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This project refers to an Arduino sketch which with the help of an external light sensor (e.g: photoresistor) can control the rotation speed of a DC motor.

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This project refers to an Arduino sketch which with the help of an external potentiometer (input device) can control a bar graph of many LEDs. Finally, when the sketch starts running, it calibrates the potentiometer (and so there should be a spin at both ends manually).

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Within the framework of the course “Numerical Methods in Programming Environments – Theory” (Department of Informatics and Communications, T.E.I. of Central Macedonia) we were asked to develop an optional program that implements Müller’s numerical method for finding the root of equations of the form f(x) = 0.

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This project refers to an Arduino sketch which with the help of an external potentiometer (input device) can control the rotation speed of a DC motor (output device). Finally, when the sketch starts running, it calibrates the potentiometer.

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A nice problem that intrigued me is the “Rubik’s Magic”. I could solve the problem fast enough. In the beginning, I thought it to be quite difficult. But I finally was able to join the three rings with little effort.

I will always post my best solutions on this post. I try to set up personal records.

Surely, I can not compete with the champions but I think I will one day reach their standards with continued practice.

Personal record: 5 seconds.

Since I got my hands on Rubik’s cube, namely the classical one (3x3x3) I got hooked on solving it. I tried several times to solve it but more often I smashed it on the wall or give up.

But recently I learned that Rubik’s cube is solved with algorithms. So when I learned the algorithms and the solution methodology, I started with good intentions. So after a while, I could solve it by applying the algorithms. I have also solved the cubes with 2x2x2, 4x4x4, 5x5x5 and 6x6x6 dimensions. Knowing how to solve these cubes, you can solve any major dimension ones. In larger cubes, there are likely more parity errors. This does not prevent you from solving them.

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This project refers to an Arduino sketch that implements a simple fire alarm using a temperature sensor, a piezo speaker and one LED as indicator for deaf-mute cases. The alarm checks every second if there is enough room temperature (via the temperature sensor). If there is enough temperature to consider it a fire burning in that place, then the alarm produces a musical tune with the piezo speaker and lights the LED indicator. Otherwise, both the speaker and the LED indicator remain in state OFF.

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This project refers to an Arduino sketch which with the help of an external potentiometer (input device) can move the position of a servo motor (output device) clockwise or counterclockwise. The system also features two LEDs which – each time the value of the potentiometer changes – change their brightness in such a way that it is obvious in which side of the servo motor are.

For example, when the potentiometer is in the extreme left position then the left LED is lit 100% while the right one 0% (or vice versa). Finally, when the sketch starts running, it calibrates first the potentiometer.

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It was a very interesting experience for me to participate in the mission of the Department of Informatics and Communications of the T.E.I. of Central Macedonia in Thessaloniki, where the Department took part in the Infosystem 2009 exhibition.

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This project refers to an Arduino sketch which with the help of an external light sensor, as e.g. a photoresistor, one can move the position of a servo motor clockwise or counterclockwise.

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Within the framework of the course “Visual Programming – Theory” (Department of Informatics and Communications, T.E.I. of Central Macedonia) we developed a clinic management application as a semester project.

The database of the application was implemented in Microsoft SQL Server and the graphical user interface in Borland C++ Builder.

More specifically, this application enables the end user to manage different patients, visits, appointments, diagnoses, treatments, prescriptions, tests, links.

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Rubik’s 360 Sphere is quite interesting. Once you understand how it works, the solution is then quite easy. Specifically, you need to concentrate your attention on the two axes as well as the two pendulums that are found inside the spheres.

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This project refers to an Arduino sketch which moves continuously a servo motor but without the help of the pre-developed “Servo” library but by direct communication, sending the appropriate PWM output to the motor. That way you have clearly complete control of the servo motor, saving enough memory and achieving better response times with less delay.

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The project ‘dec2bin’ (decimal to binary converter) is the implementation of an idea I had for some time. I have to admit that sometime in the past when studying possible ways of programming embedded systems with the programming language C and C++, I felt the need to be able to produce, through a program, supposed memory addresses in the form of binary numbers.

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A beautiful and dynamic experience that I hope will be repeated again.
Congratulations to the organizers and participants of this conference.
Their contributions to Free Software was invaluable.