Minimodem – general-purpose software audio FSK modem
whence.com
whence.com
I wanted to experiment with using a mic-array in order to improve the SNR. Got a 4 Mic ReSpeaker [0] some time ago, but haven't played with it yet. My expectation is that capturing the audio simultaneously with multiple mics should reduce the noise and thus improve the robustness of the transmission allowing to increase the bandwidth.
For example at a grille during the game.
FWIU, e.g. Chromecast have ultrasonic pairing.
Actually, the "Waver" youtube video linked at the top of the README has an embedded ultrasound transmission at around 0:36. I can for example decode the message on my iPhone by simply running the Waver app and playing the video on my PC.
Some people have already done some work for AV sync in the issues of the project [0].
> The I2S is a small, low-cost MEMS mic with a range of about 50Hz - 15KHz, good for just about all general audio recording/detection.
From https://en.wikipedia.org/wiki/Ultrasound :
> Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.
Raspberry Pi Pico (RP2040), Pi Zero [2 W]: $5+
Power supply, case, wall-mount:
Mic: ~$6
Huge [red] 7-segment display with I2C and voltage regulator components taped to the wall next to the sports bar TVs:
The same issue affects radio time signal (e.g. https://en.wikipedia.org/wiki/Greenwich_Time_Signal, last beep is the exact top of the hour), so some broadcasters will no longer play them on internet streams/digital radio, rather than be inaccurate.
Selecting between multiple audible [sports bar TVs, radios] might imply need for a sonewhat-unique signal code, or only over e.g. USB would work with more than one game on; because there's naturally noise in that airgap channel.
Also, it was only a few days ago I finally learned that modem is short for MOdulator DEModulator. My mind was blown.
I think ham radio licenses lost popularity between then and approx 2018. Demonstrating fluency with Morse was necessary for a license long ago. Nowadays, there’s a renewal of interest but many new Ham operators can write a Morse codec faster than they can learn fluency by hand. I think the requirement for demonstrating Morse by hand in order to obtain a HF license will be dropped if it isn’t already.
The Morse requirement was dropped by the FCC for all license classes back in 2006.
But even with SDR making radio experimentation easier and more rewarding than ever ham radio seems to be continuing its slow decline and the average age of operations continues to rise... and we continue to lose spectrum (e.g. we just lost the 9cm band).
I don't imagine any QAM-like stuff working. FSK does, but the transitions get a little wonky, and the different frequencies will often have different phase shifts. ASK modulation should work, but haven't gone there yet.
But its interesting. I know a thing or two (literary) about encoding in the radio spectrum, but none of the encodings I've found deals with systems that are so un-lineary.
Asking because I want to send single characters (or two) from a controller.
It should be noted that any signal that can be modulated and demodulated can be used to exchange information, so either visible or IR light, ultra/infra sound etc. It's just a matter of building the right hardware interface.
Ie. I want to fit a few hundred bps of data inaudibly into some nice classical music.
It could be hidden up at 18kHz, but to be honest that still sounds nasty for those of us who have ears that still work that high.
Better would be to hide the data in harmonics and neighbouring frequencies of the music. Human ears, if they are hearing a sine wave at frequency X have reduced sensitivity for audio at frequencies close to X and close to multiples of X. I think you could use that effect to send data much more pleasantly.