Pokorinta : All-in Cajon

Pokorinta – A cajon that plays itself.

Pokorinta is a cajon-style automatic rhythm machine. Unlike a typical cajon, it houses multiple instruments such as tambourines and cymbals inside its compact body. Despite its size, it can produce a wide variety of sounds similar to a full drum set. Seven electronically controlled solenoids rhythmically strike these instruments to create lively and natural rhythms. Because both the instruments and the control system are integrated into a single enclosure, we call it the "All-in Cajon."

Demo Video (YouTube):

Background & Motivation

The project began when one of our band members tried practicing the cajon. However, keeping steady rhythms for long periods proved to be difficult, and progress soon stalled. Playing simple, repetitive beats endlessly is not easy for a human performer. This sparked the idea: what if a machine could take over the role of keeping perfect time? By combining electronic control with solenoids, we could achieve precise, unwavering rhythms.

Moreover, since the solenoids—not human hands—are doing the striking, we were no longer limited to mounting instruments on the outside of the cajon. This allowed us to place cymbals and other instruments inside the enclosure, giving Pokorinta its unique all-in-one design.

Features

• Pressing the button on the main unit starts the performance.
• Performance data uses MIDI files stored on an SD card. The data from drum channel (9) is read, and each drum instrument is mapped to Pokorinta's solenoids for playback.
• By reflecting the MIDI note “velocity” into the PWM duty cycle of each solenoid, Pokorinta can express dynamics in volume.
• Since each solenoid has a different mechanical response time from electrical drive to sound production, the software applies timing compensation to synchronize the overall rhythm.
• These technical refinements allow Pokorinta to reproduce rhythms that sound as natural and expressive as if they were played by a skilled human drummer.

Use Cases

• Live performances and stage shows: Pokorinta can provide a unique automated percussion performance that enhances the visual and auditory experience.
• Practice companion: acts as a reliable rhythm partner for musicians practicing alone.
• Leisure facilities, bars, and parties: Pokorinta can provide background music (BGM) through automated live performances that add atmosphere to venues and gatherings.

Future Prospects

• Continue expanding the variety of sounds by adding and adjusting internal instruments, while maintaining the compact enclosure—aiming to approach the expressiveness of a full drum set.
• Explore a transparent enclosure design so that the striking solenoids and internal instruments can be clearly seen during performance, allowing audiences to enjoy the show visually as well as aurally.
• Improve the user interface: instead of only starting with a switch, enable remote operation or allow Pokorinta to start automatically by detecting the sounds of surrounding band members.