Most Raspberry Pi projects we feature debut privately and with little fanfare – at least until they’re shared by us.
The El Carrillon project, however, could hardly have made a more public entrance. In September 2019 it was a focal point of Argentina’s 49th annual Fiesta Nacional de la Flor (National Flower Festival), where its newly overhauled bell tower proudly rang out a brand-new, Raspberry Pi-enabled tune.
Many years ago, festival organisers created custom hardware with a PIC (programmable interface) microcontroller to control 18 tuned bells. Each bell is associated with a musical note, from A3 to D5 with all the semitones. Until its long overdue update, the tower’s 18 bells had rung the tune to Ayer, also known as Yesterday by The Beatles. They now have a brand-new repertoire of MIDI-based tunes, including the theme from Star Wars.
For Gerardo Richarte, the originator of the project, there was a little extra pressure: his dad is on the board of the NGO that organises Fiesta Nacional de la Flor, and challenged his son to come up with a way to update the bells so different songs could be played.
Ringing the changes
With the challenge accepted, Mariano Martinez Peck explains, “We chose Raspberry Pi because it was inexpensive, yet powerful enough to run Linux, Python, and VA Smalltalk. We could find ready-made HATs that actually matched the pinout of the existing flat cables without much hacking, and only a minimal amount of other hardware was needed. In addition, there was plenty of documentation, materials, tutorials, and GPIO libraries available.”
The bells had a pre-existing driver module
The project aim was to be able to run a mobile-friendly website within Raspberry Pi Zero that allowed control, configuration, and playback of MIDI songs on the bell tower. “In addition, we wanted to allow live playing from a MIDI keyboard,” says Mariano. The project developed as a live test and iteration update, but the final build only came together when Mariano and Gerardo’s moment in the spotlight arrived and El Carrillon rang out the first new tunes.
Coding a classic
The decades-old chimes were controlled by assembly code. This was superseded by Python when the team made the switch to Raspberry Pi Zero. Mariano explains, “Raspberry Pi allowed us to use Python to directly interface with both the old and new hardware and get the initial project working.”
However, the Python code was itself replaced by object-oriented VA Smalltalk code – an environment both Mariano and Gerardo are adept at using. Mariano says, “Smalltalk’s live programming environment works really well for fast, iterative development and makes software updates quick and easy without the need for recompilation that lower-level languages [such as assembly or C/C++] would need.”
El Carrillon’s bells can now play any MIDI file on Raspberry Pi, and the notes of the song will be mapped to the tuned bells. However, as the testing process revealed, some songs are more recognisable than others when reproduced on chimes.
A final feature enabled Gerardo to bag some brownie points with his father-in-law. He recently added a web interface for controlling, configuring, and playing songs, meaning the bells can now be controlled remotely and the song selected via a smartphone app.
The El Carrillon bell tower forms a striking backdrop to the flower festival and other cultural events
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