In 2012 we had to form a team of three people for a project that would last a few months. Teachers had multiple subjects from which we could choose. With my team, we chose the study of analog and digital data. We thought it was a very good subject because it had so much potential. We could talk about so many things, we could even make a little experiment, which we did.

In the report we gave our teachers at the end, we mainly traced the history of analog signals and devices, and explained how and why it has been slowly replaced by digital technologies. We also talked about how analog signals work, by taking an audiocassette as example. Concerning the explanation about digital signals, we took an audio CD as an example. We also talked about binary, Joseph Fourier transform, and Nyquist-Shannon sampling theorem.

The motivation we had permitted us to finish the report before the due date. Therefore, our teachers proposed we make an experiment related to our research. The problematic was the following : "How can we try to convert analog to digital with what we had at school ?" We thought about it a while before finding what we could do.

In order to respond to the problematic, we first had to do something that would work like an analog signal. We first learned about notes and their frequency. That way, we would be able to reproduce the melody of a real song.
With excel, we managed to convert frequencies to "zeros" and "ones" like this :

Thanks to the formula above, we could write any frequency on column B, and it would convert it as black stripes or leave the cell blank. The black stripes were the 1 and the empty white cell was the 0.
After that, we used sensors that would see the black or white and make a difference between the two. The sensors were these :

We had two sensors, so the six columns of the excel file where there are the black and white cells would be read. Now we had two things left to do : finding a way for our sheet of paper to be read smoothly by the sensors, and converting what was read by them as actual sound.
We solved the first problem by using an old printer to which we removed the unnecessary parts :

Here we could place our sheet of paper and the sensors. We took the cables of the small motor and soldered them onto a voltage regulator so we could control the speed. We also added a piece of wood so we could place the sensors. Now the only thing left was to convert what the sensors would read to actual sound.
This was done with a software called LabView, which works with data acquisition cards :

Now we just had to connect speakers to the computer, put the sheet in the printer, and the frequencies we chose on the excel file were playing. We could modify it to make other melodies.

When seeing how well it worked and how my team and I were involved in the project, they proposed us that we present it to an event called "olympiads of engineering and science" which was taking place in an engineering school. We would present our project to 2 different boards of examiners, and meet other contestants and talk with them about our project and theirs. We did not win in the end but we were very happy and thankful for the opportunity our teachers gave us.