A proof-of-concept to transfer bitcoin sats as ecash via sound using the Cashu protocol.
Ecash can be sent digitally as text data, visually via a QR code reader, physically as a piece of paper with text or a QR printed on it. How about audibly? Can ecash be sent via sound?
This will use psk31 as the text-via-sound protocol. psk31 is similar to Morse Code, except that psk31 allows for upper and lowercase characters which is necessary for a Cashu token.
To try to receive these 21 sats as ecash, you'll need the following:
Receiving data using Fldigi looks like the gif below:
Just to explain what's going on here: a sound file is playing. You cannot hear it in the gif, of course, but there was sound playing audibly when the video was captured. My wife confirmed that it is an annoying sound. 🙂 On Fldigi, I set the Op_Mode to "psk31". The microphone on my computer is picking up the sound. Fldigi "shows" the audio in the "waterfall", the blue stream underneath "2000" in the gif. The red bars are the "tuner" to pick up the blue stream, I manually slid it over to the stream. Fldigi then simply decodes the sounds into text. This is how you will "hear" and see the Cashu token.
I tested the process successfully. I copied the token from Fldigi and used cashu.me to RECEIVE-->ECASH and pasted in the Cashu token. The token came back as valid. I did every step except "RECEIVE" the ecash. See image below. In other words, this should work.
Note that if the token has already been claimed by someone, you will get an error such as below:
Will this be the "world's first" ecash sent via sound? I don't know. Still, is has a nice ring to it and maybe you can be a small part of ecash/bitcoin history. 😀
On June 20, 2024, 21 bitcoin ecash sats were successfully sent as Cashu tokens via sound. Ecash-via-sound was successful! 😀
Since it's completed, I'll paste the Cashu token below that was/is transmitted in the sound file. If you wish, you can copy/paste it into a Cashu wallet. It won't go through, but this shows that it was successful. Cashu.me is an easy in-browser wallet for this.
The ecash-over-sound challenge message was originally put out in three places:
Some great discussion was spawned on (1) the Stacker News page above (as well as this reply animating an ecash receive) and (2) also on this Nostr thread. Things like possible payments via sound and data transfer beyond human hearing were discussed. And, a Morse Code Cashu token was broadcast.
What's next? I'd love to see an ecash-transmitted-by-light project!