Text Entry Using Single-Channel Analog Puff Input
Adam J. Sporka · 2014 · Proceedings of the 16th International ACM SIGACCESS Conference on Computers & Accessibility (ASSETS 2014) · doi:10.1145/2661334.2661423
Summary
This short demonstration paper presents a prototype text entry system that repurposes a single-channel analog puff input device — specifically the AKAI EWI USB, a MIDI controller designed for woodwind instrument emulation — as an assistive technology for people with motor disabilities. The device quantifies airflow on a scale from 0 to 127 via MIDI controller messages (CC2), providing continuous analog pressure data at interactive rates. The author built a Windows application that displays a static on-screen keyboard arranged in a grid where characters are ordered by English letter frequency, placing the most common letters in the top-left positions to minimize cursor travel. The interaction model uses a two-puff selection process analogous to operating a claw crane machine: the first puff moves a cursor horizontally to select a column, and the second puff moves it vertically to select a row. The cursor moves continuously while the user blows, and the analog nature of the input allows the user to control cursor speed by varying breath intensity. When the second puff ends, the character under the cursor is entered as a keystroke. The system also uses maximum airflow as a cancel/reset command — useful when the user overshoots a target, since the cursor can only move in one direction per axis. A sustained maximum-flow gesture of at least 0.5 seconds triggers a backspace function.
Key findings
An informal evaluation showed the system could achieve a text entry rate of approximately 5 words per minute (25 characters per minute) after brief training, with an error rate of about 1 incorrect character in every 10 entered (10% uncorrected error rate). The key innovation is the use of continuous analog airflow data rather than binary sip/puff signals, enabling proportional speed control during cursor movement. The frequency-based character layout reduces average cursor travel distance for common English text. The system requires only a single input channel — one breath sensor — yet supports column selection, row selection, speed modulation, cancellation, and backspace through different airflow patterns and intensities. This stands in contrast to prior puff-based text entry systems like PuffText, which relied on discrete breath signals for simpler selection mechanisms.
Relevance
This prototype demonstrates that even a single analog breath input channel can support surprisingly rich interaction when the signal is interpreted creatively. For accessibility practitioners, it highlights the potential of repurposing commercial music hardware (MIDI controllers) as low-cost assistive input devices, bypassing the need for specialized and often expensive assistive technology. The 5 WPM entry rate is modest compared to standard keyboards but meaningful for users with severe motor impairments who may have very few input options. The work contributes to the broader research agenda of expanding text entry possibilities for people who cannot use conventional keyboards, pointing toward future improvements through predictive text, adaptive layouts, or multi-channel breath input.
Tags: sip-and-puff · text entry · assistive technology · motor disabilities · alternative input · scanning · MIDI · analog input