Post #1849701
2026-02-13 16:08 UTC
Update: after heavily optimizing the Goertzel algorithm (in ARM assembly of course) it's now at ~18 frequencies that can simultaneously be detected (4.2MHz chip, 35000 samples/sec, 100 times per second). That appears to be about as far as I can push it. Note that in the above post I probably used a sample rate of 25000 which needs fewer cycles to process.
Next up: defining some sort of framing format with preamble so the receiver can lock on to the signal and calibrate the various frequencies. And see how much data can actually be sent over sound without getting lost in noise.
Replies (1)
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@ayke@hachyderm.io 2026-04-30 18:45
Update: now at ~200 bytes/second! That's 1.6kbit/s. It will need some error detection and correction which will lower the bitrate a bit but this is looking promising. Depending on the speaker the signal is nearly noise free which might mean I could even increase the bitrate. The goal is still to enable programming the earrings via audio and it looks totally doable.