Our client interconnects a Roland FR-1xb V-Accordion with a Roland E-A7 keyboard arranger which both support the MIDI protocol.
The accordion lacks buttons to control the arranger accompaniment. Moreover our client doesn’t use the sounds of the accordion but those of the arranger but the accordion has only buttons to select some predefined sets.
By interconnecting an Arduino (with the Olimex SHIELD-MIDI) between the accordion and the arranger, we have been able to map the accordion buttons to the required arranger functions. Our client is now able to switch to a control-mode (à la VI) on the accordion into which the note buttons can be used to select a variation or an ending of the accompaniment.
The overall cost of the different parts was about 50€. It is cheaper and more versatile than the existing “MIDI event processors” (but it lacks a nice box).