Sacred Engineering: The Modern Pipe Organ Setzer
In the world of classical music, a Setzer (or combination action) is a sophisticated control system that allows an organist to instantly change the "Registration" (which pipes are active) with a single button press. This project transforms a traditional pipe organ into a MIDI-capable instrument using the Arduino Uno, providing a digital memory for thousands of pipe combinations and automated Crescendo control.
I/O Expansion via PCF8574
A pipe organ can have dozens or even hundreds of stops (registers). The Arduino Uno alone does not have enough pins to control such a massive array. This project solves the "Pin Bottleneck" using the PCF8574 I/O Expander:
- I2C Efficiency: Using just two pins (SDA/SCL), the Arduino can interface with multiple PCF8574 chips. Each chip adds 8 digital I/O lines, allowing the system to scale to control the entire organ console.
- Non-Volatile Memory: The Setzer settings (presets) are stored in either the Arduino's internal EEPROM or an external I2C memory chip, ensuring that the organist's carefully curated sounds are not lost when the church power is turned off.
Crescendo and Specialty Logic
Beyond simple On/Off switching, the Setzer handles the Crescendo Pedal:
- Stepped Activation: As the organist depresses the crescendo pedal, the Arduino gradually activates more and more pipes, providing a smooth increase in volume and "Brilliance."
- Back-EMF Protection: Since organ registry switches are often large inductors (Solenoids), the project utilizes 1N4007 Diodes. These "Flyback Diodes" protect the sensitive Arduino and expander chips from the massive voltage spikes generated when a pipe stop is deactivated.
- High-Speed Response: The use of a 16 MHz Resonator ensures that the MIDI messages and stop transitions happen with zero perceptible latency, a requirement for world-class musical performance.
Custom PCB Implementation
Due to the high number of connections required for an organ registry, standard breadboards are insufficient. The author provides custom PCB designs (via EasyEDA) specifically for a "Setzer 24-reg" layout and a "Microswitch Strip" for the physical registry keys. This professional-grade approach ensures the mechanical reliability needed for an instrument that may be played for decades.
Device based on Arduino Uno, along with expander PCF 84. Turns on and off registry in pipe organs, and remembers settings. It also supports crescendo.
I ordered printed circuit boards from Chinese. Here are the links to the diagram and boards:
https://easyeda.com/rommil67/setzer-24-reg
and board a microswitch strip for registrer key.
https://easyeda.com/rommil67/listwa-pod-registry