So I’ve built this thing:
And I’m reasonably happy with it – it’s a fairly simple construction, laser cut boxes + vinyl cut stickers.
The internals consist of a Raspberry Pi Pico with a limit switch and RFID reader. Each disc has a small adhesive RFID tag. When the disc is inserted, the limit switch closes and triggers the RFID reader to check the ID of the tag which can be used to play the appropriate track.
The tracks are stored on, and played by, this MP3 player – which I’ve used before and overcome its myriad quirks (more on that in another post).
The MP3 device is powered by a 3V pin on the Pico. It worked great while building – discs were tested extensively during construction. I even found a tag that seems compliant with specs but would not register with the Pico’s RFID reader for some reason and had to be replaced.
I discovered an issue upon connecting the device into an external power source, rather than my laptop – around 30s into a song, the unit would just cut out. Suspecting power, I changed the cables and chargers to no avail. Connecting the Pico back into my laptop resolved the issue.
Curious.
The Pico has 3 different options for providing power:
- 3v Pin for, well, 3 volts
- VSYS for 5 volts – my understanding is that this is the main supply to the Pi and may actually vary below 5 volts
- VBUS for… 5 volts again. This is straight from the external power though.
I was powering my MP3 player via 3V, and while the current required by the player should not have been more than the Pi can provide, I suspect it was either fluctuating below 3V or tripping something in the Pico itself. Connecting the player directly to VBUS seems to have resolved the issue (thankfully the player can handle anything from 3-5V).
Just something to remember next time weird things start happening when connecting to a new power source.