Here we go...all the sounds that you have collected over the years can now be heard from your railroad. In this article you will wire a sound playing module to a speaker and a Nano with 6 wires. Imagine a button to announce the next train ready to leave, a light sensor noticing a stock car at the loading chute making some cattle noises, wheels squealing around a curve, or on my layout, elephants and lions in the wild! DFPlayer Mini pinout So, save some sounds, (or “songs” called from here on), in MP3 format, onto a micro (u) SD card using your personal computer. Reading the documentation makes it a bit confusing, from: the order matters in which you drag the files to the uSD card, to: having 100 folders with each 255 sounds and commands calling which file in a folder?!? What I did was save my sound files as 001.mp3, 002.mp3 and so forth in the root folder of the drive, and had no trouble getting them to play. Remember to properly “Eject” the card using your operating system