Eventually I will write a blog post. The software is actually not much, just some basic Arduino stuff. I am using an ESP32, a full size SD card board and a VS1053 board (both connected via SPI). The software is currently just trying to read from the SD card in a loop and when it can it just plays the MP3 files in order. Other things that are not connected to software is a Li-Ion battery, charger circuit, step-up converter, LM386 based amplifier circuit and a speaker :)