Commodordion: Two C64s, an old floppy and a band make an accordion

Tinker Linus Akesson is a passionate accordion player. For the past three and a half years, he’s been building his Commodordion out of two old C64s, some floppy disks and some decorative tape. The device is now complete and fully functional.

Akesson demonstrates the device in action on YouTube. He also explains some of his ingenuity.

So he wanted to adapt the playability to that of a real accordion. To do this, he first experimented with volumetric flow meters similar to those used in cars. However, the measured values ​​achieved with it were not sufficient for volume control. In principle, the resistance heating element is kept at the temperature and cooled by the air flow. Thus the flow of cooling air can be measured indirectly using the current required to maintain the temperature. However, Akesun did not want to burn anything and at a temperature of 50 ° C the solution was unusable. It was too slow to respond to changes in airflow.

In the description on his website, Akeson explains that he now uses a microcontroller to measure the volume of airflow hitting the microphone using a threshold value (loud or not loud corresponds to 1 and 0) and collect 512 samples as a basis for taking the volume control. On top of that, it forms a running medium and increases signal filtering – otherwise noise from the microphone may end up in the audio output. Akesson mixes the audio output of both C64s together after adjusting the volume using the above mechanism and converts it to an analog output signal via a 12-bit DAC.

The instrument also mimics the proper functions of an accordion in other respects: one side plays the strings or accompaniment, while the other is responsible for the melody. Akesson has also added a programming mode in which he can record loops of music and then modify their pitches, for example.

(DMK)