Interesting, though before clicking I thought the headline might be referring to a very poorly paid presentation about Marvel movies.

Nice work. Especially referencing the TI prior art of the Speak and Spell. This kind of synthesis was quite prevalent in the early 80s - school BBC Micros had a ROM which let you "*SAY" a phrase. Classic Macs had MacinTalk.

Another codec which might be interesting to try but is considerably more complicated is AMR, from GSM: https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_code...

This is great. Missed opportunity for a low-pass RC filter on the speaker circuit - if you know you're driving an 8kHz sample rate, you can design your filter with that cutoff, and it'll sound way better (it'll get rid of the buzzy quality).

Could hang an i2c flash chip off that thing for more storage and still have enough IO pins for serial coms and a spare IO pin.

You should be able to do it all on-device, check out SAM, the Software Automatic Mouth. The actual data in the *_tabs files:

https://github.com/ctoth/SAM/tree/master/src

I saw another audio project on the same microcontroller (family) posted a few days ago: ModPlayRISCV It plays a tracker MOD. using PWM with a low-pass filter. It resamples/scales all samples at varying rate/volume into a ring buffer which gets fed to the PWM comparator by DMA.

https://github.com/cpldcpu/ModPlayRISCV

First I thought you made a lecture on MCUs which was available for viewing in exchange for $0.10

Then I thought you made a lecture on MCUs where the device was available for purchase generally for $0.10.

Then I thought with an MCU valued at $0.10 you generated speech

English... sigh

> I considered a few encoding options for compressing the audio.

The presentation of this part seems extremely padded out to me, ironically enough.

These CH32 mikrocontrollers are great and dirt cheap. I've build a small DC motor controller with them to control a robot: https://github.com/h0lad/MiniSpeedController

The bigger ones have PHYs for USB HS, USB-C (5Gbps) and 10/100M Ethernet integrated (!). And their development environment (Mounriver Studio) isn't too bad - I didn't had the immediate urge to port everything to CMake/VSCode.

But they need some kind of pin planning tool. It's awful to use the datasheet and find the correct pin functionalities and their mutual exclusions... STM32 mastered this with their STM32CubeIDE tool: select a feature (like USART1) and the right pins light up - alternate pins are easy to locate.

They also should clean up their license mess on OpenWCH (their GitHub page). Lots (all?) of their HALs are Opensource - but the right version with right SPDX tags are often a bit hidden.

Can you export the schematic and Gerber files to a PDF file? A lot of open source projects do this, and it makes it much easier to tell what's going on, with software pretty much everyone already has on their computer.

It's probably worth mentioning the 2400bps (300 bytes per second) LPC10 codec built into SoX. If you have SoX installed, try

    rec -t lpc10 speech.lpc

and then speaking into your microphone for ten or fifteen seconds before you ^C it. Then play it back with

    play speech.lpc

It will sound very robotic but pretty comprehensible, at least with an adult male voice in English, and it preserves a lot of the prosody and enunciation that is so hard to get out of speech-synthesis packages.

12KiB of data at 300 bytes per second would be 41 seconds of recorded speech.

Decoding the LPC10 data on the CH32V003 might be tricky. On amd64, running `make CFLAGS=-Os` followed by `ld -r -o tmp.o *.o` inside sox-14.4.2+git20190427/lpc10 yields a tmp.o with 25243 bytes of text (including .rodata, etc.) and 356 bytes of data. I'm not optimistic that RISC-V would compress that to fit inside the CH32's flash. And I find the code in that directory inscrutable; it's Fortran that's been compiled to C.

Still, it seems plausible that you could massage the LPC10 data into a format that something like Talkie would understand.