Quieting Down A Bandoneon Accordion With MIDI

The bandoneon, known as the tango accordion, is quite a loud instrument to practice within the confines of an apartment, and could possibly lead to some neighborly disputes. [HLB] enjoyed playing his but wanted a way to turn down the volume a bit without, in consideration to his neighbors. Instead of building a whole soundproof room, he decided to throw Arduino’s and MIDI at the problem.

Bandoneons, like all accordions, are operated by pushing air from manually pumped bellows through a series of reeds, which are each opened and closed by a valve mechanism. [HLT] turned each valve lever into a simple on/off switch by attaching a magnet, with hall-effect sensors on long custom PCBs next to each row of valves. The hall effect sensors are connected to I2C I/O expander ICs which connect to an Arduino Nano, one for each side of the instrument, which sends out MIDI messages via serial. Everything is mounted inside what looks like quite an old instrument with Blu Tack to avoid having to make a lot of permanent modifications.

The bandoneon still functions normally with no permanent modifications, so to play with MIDI-only the bellow is simply not pumped. This means [HLB] can’t modulate the MIDI velocity (loudness) while playing, which he admits is a limitation but better than not playing at all. He does, however, note that he could add a pressure sensor inside the bellow if we wanted to add velocity to the midi output when neighbourliness isn’t a consideration. On the audio output side [HLB] built a small stand-alone synthesizer with an Odroid SBC running FluidSynth and a HiFi shield.

We think this in a well-executed solution to a real problem, without overdoing it on the tech side. All the details, including KiCad PCB files and Arduino code, is up on Github, so feel free to use and modify it to build on your own musical talents.

Almost every instrument can be adapted to output MIDI, and in the past few decades it’s has actually become a core part of massive, building-sized pipe organs.

9 thoughts on “Quieting Down A Bandoneon Accordion With MIDI

  1. Thank you for the project! Accidentially, I am currently working on a similar project, having an old bandoneon with damaged tongues. As it is not chromatic, I use a diferential pressure sensor (sensirion SDP811) for direction and velocity, so have different notes for each button.

    Instead of hall sensors, I use micro switches. As I/O expander I have four MCP23017, and the MCU is a ESP32 development board. I selected this one to be more flexible (and, of course, have more CPU power).

    As I wanted to be wireless, I first tried to use bluetooth (BLE-MIDI), which worked fine – but the latency was too high, as the ESP32 BLE implementation does not allow for short transmission intervals. After trying different other implementations, I ended up with AppleMiDi, aka RTPMidi. This really works fine, when directly connected (the bandoneon acts as WiFi access point, the synth connects as WiFi client); using a different access point may increase the latency.

    To not have to open the instrument too often, software updates are done via OTA, and configuration is possible via inbuilt web server.

    I also thought of having different channels for left and right side to enable different instruments (not yet ready).

    In the bass side there is a LiPo with battery control, so there is no power cable needed. The only visual changes are a power jack to load the battery and a small switch to power on/off. Playing the instrument feels nearly normal: velocity and pitch bend are influenced by the air pressure (still struggling with the best functions), only the pressure sensor leaks some air.

    As soon as I’m finished (still have to complete the right hand side), I could document the hard- and software, if you are interested.


    1. Hi Richard,

      Thank you for your comment. You project sounds nice, it gives some clues since I think wireless really make sense. And I would go for a pressure sensor if owned a second instrument where reeds would be “stuck” in order to be silent when using the bellow.

      I eventualy found another interesting project about a full 3d-printed MIDI bandoneon made by Uruguayan students (https://github.com/jebentancour/Bandonberry). I could barely find a video of the instrument but that would be a good tool for practicing quietly (https://twitter.com/search?q=bandonberry&src=typed_query).

      I would be highly interested in going through the documentation of your project.


      1. Thank you for the link. This is a very new approach, but I can’t imagine how it feels to play this instrument…
        And for me, it is way too complicated. I only can make simple projects, so mine is really simple in hardware ans software. At first I thought of having an amplifier and speakers on board; but with regard to power consumption and the possibilities of external synthesizers I preferred MiDi.

        And in my case: Please remember, this was an old and defect Bandoneon not worth rapairing, so I removed the reed blocks. That way I could put the microswitches into the now accessible holes. Do not do this with a working bandoneon!

        1. Hi Richard,

          Indeed a very nice project, congrats! We both should have shared our projects earlier…

          I really like the wireless aspect and thus all the researches you made to figure out the most efficient way to make it. I will (slowly) turn my bandoneon wireless.

  2. This is a very nice setup. May I suggest that perhaps you can have a large hole punched somewhere so the air cane come in and out through it instead of the reeds (should be of course closable) and then you can add a flow sensor to detect the speed of the air movement and direction.

    1. Hi Carlos,

      Well, bandoneon already have a right-thumb-controlled “large hole”: it is made for closing the bellow back. But using it for quieting does not operate: it completely changes the feeling of the bellow. The best solution I found for making the instrument more quiet is covering it with a sleeping bag…


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