Simple ESP32 SD audio player (internal DAC / PDM)

WAV library: https://www.xtronical.com/basics/audio/digitised-speech-sound-esp32-playing-wavs/

A github project that probably plays a wav file: https://github.com/LilyGO/TTGO-T8-ESP32

A micropython project playing WAV (though I'm quite sure I read somewhere that the internal DAC wasn't yet supported on micropyton): https://m5stack.hackster.io/lukasmaximus89/play-wav-files-on-your-m5stack-3bee7e

internal *ADC* code: https://github.com/espressif/esp-idf/commit/2fceec4d858c62a489496678c765ae1a2d68645c

Well, I started typing, and then lost everything.

There are some projects on hackaday that have simple audio output (and even video), but none of them connects to a speaker directly.

This is how I connected my SD card:

https://github.com/espressif/arduino-esp32/tree/master/libraries/SD

There's this project that does PDM: https://github.com/karawin/Ka-Radio32. It tells to connect a speaker to GPIO 25 for PDM/internal DAC, but I think that would way exceed the 12 mA of max output current.

I found a 40xx/74xx logic buffer circuit for PDM sound somewhere (lost the link...), and a mention that a MOSFET would be a good idea. Somewhere else I found adding a 100 uF / 47 uF capacitor between output and speaker should do the trick.

There's this video:https://www.youtube.com/watch?v=oCmfpJNDPn8 that shows an ESP32 with audio out over PDM

This shows something about how to use PDM: https://github.com/earlephilhower/ESP8266Audio/issues/138 (and also notes that for a long time, PDM hasn't worked)

This project also mentions PDM: https://github.com/MrBuddyCasino/ESP32_MP3_Decoder. The source seems based on Ka-Radio32 - or probably the other way around.