Commodordion: two C64s, old floppy disks and tape make an accordion

Tinkerer Linus Akesson is an avid accordionist. For the last three and a half years he has been fiddling with building his Commodordion out of two old C64s, some floppy disks and some sticky tape. The device is now complete and fully functional.

Akesson demonstrates the device in practice on YouTube. He also explains some subtleties that have occurred to him.

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

In the Description on their website explains Akessonwhich uses a microcontroller to take the volume of the airflow hitting a microphone using a threshold value (high or not high depending on 1 and 0) and the sum of 512 samples as the basis for its volume control. Above this, it forms a moving average and further filters the signal; otherwise, microphone noise may end up in the sound output. Akesson mixes the sound output of both C64s after adjusting the volume using the above mechanism and converts it to an analog output signal through a 12-bit DAC.

The device also mimics the correct functions of the accordion in other respects: one side plays the chords or accompaniment, while the other is responsible for the melody. Akesson has also added a programming mode where you can record music loops and then modify their pitches, for example.

(DMK)