Brushing Interface
The Brushing Interface is a novel musical instrument that detects the movement and pressure of drawing and writing tools on its surface. Its exterior wooden structure is topped with an acrylic sheet housing a sensor grid and a piezo microphone. This assembly is covered with paper, providing the surface where the performer draws, brushes, or writes during a performance. The core circuitry posits inside the body of the instrument.
Works Using this Instrument
Brushing Improvisation – N°2 (2023)
Drifting (2022)
Technical Info
The key technical engineering involved in this project was implementing the pressure sensor grid using a custom, DIY approach. Commercial FSR sensors cost around $5 per 2 cm square, totaling over $1,000 for a full set. This was obviously not economically feasible. Furthermore, using proprietary sensors made it impossible to customize their shape and size, imposing a significant constraint on the creative process.
Therefore, a critical first step was to build a reliable and affordable FSR sensor from scratch. FSRs (Force-Sensitive Resistors) consist of a flexible resistive layer between two conductive layers; pressing them brings the conductors closer together, lowering resistance. Existing DIY literature showed that copper tape worked well for the conductors, so the main goal was finding an appropriate piezoresistive material. Through experimentation, Velostat emerged as the ideal material due to its low price ($5 for a 30 cm² sheet) and ease of handling. The final sensor was constructed by sandwiching a layer of Velostat between folded copper tape to achieve double-sided transduction.
This sensor design proved to be extremely affordable, reliable, and sufficiently sensitive. The next challenge was connecting over two hundred of these FSR sensors to a single microcontroller. Because most hobbyist microcontrollers have at most 20 analog inputs, multiplexing was required. Specifically, I used the CD74HC4067 16-channel multiplexer (via SparkFun breakout boards). A Teensy microcontroller was selected to handle the sensor data due to its high processing power and fast sample rate, ensuring smooth, real-time data acquisition across all sensors. This allows to send all 216 sensor data through serial to the Max patch for real-time mapping. Finally, to ensure circuit reliability and clear organization, a custom PCB was designed in KiCad and professionally fabricated.
In terms of audio, it picks up friction between the writing/drawing tools and the paper through 8 piezo microphones, which is sent to the Max patch through an audio interface. Inside the Max patch the sound is processed in real-time through the mapping with the pressure sensor data input based on the composition of the piece.