ultrasonic.fyi
Ultrasonic crypto payments. Your phone & pc hears the request. No QR codes, just sound waves.
Project Description
Reimagining crypto payments using ultrasonic sound waves.
Merchants emit payment requests as inaudible ultrasonic tones (18-19kHz). Customer devices automatically detect them, decode the data, and open WalletConnect Pay.
No QR codes, no Bluetooth, no camera required.
It's tap-to-pay without the tap. Walk into a shop or conference and pay from across the room, or even fully offline like on the plane.
How it's Made
The core tech is FSK (Frequency Shift Keying) at ultrasonic frequencies - 18kHz for preamble/sync, 18.5kHz for binary 0, 19kHz for binary 1. These frequencies sit just above human hearing but within range of standard phone speakers and microphones.
Web app built with React + Vite, deployed on Cloudflare Pages. The POS uses Web Audio API's OscillatorNode to generate precise sine waves. Customer wallet uses AudioContext + AnalyserNode with FFT to detect dominant frequencies in the 17.5-19.5kHz range in realtime.
iOS app built with SwiftUI, using AVFoundation for audio capture and Accelerate framework for FFT analysis.
Backend runs on Cloudflare Workers with KV storage. WalletConnect Pay handles the actual crypto settlement.
