Screen-free audio players for children exist, but the commercial ones sit behind a paywall and a locked ecosystem, with one retail option costing 99.99 euros plus subscriptions. Nvkv Makes wanted something in the same spirit, only cheaper, offline, expandable and open, and the answer was a miniature cassette deck that feels like it came out of the eighties. Drop in a tape, and an audiobook or music starts; pull it out, and playback pauses.
The electronics centre on an ESP32-WROVER with Wi-Fi and Bluetooth Classic, an MFRC522 reader, microSD storage and a TLV320DAC3100 DAC over I2S, with a separate amplifier driving the speaker. Volume runs through a rotary encoder, and three momentary buttons cleverly share a single analog pin, told apart by voltage thresholds instead of an external expander. Firmware uses FreeRTOS across both cores: RFID polling sits on one, continuous audio streaming on the other, which cured early swipes that stuttered like a slow robotic voice.
Each cassette hides a 13.56 MHz coin tag inside printed shells, and 6 by 3 mm neodymium magnets latch the housing and door. Long-pressing the encoder opens a Wi-Fi access point with a web interface, where you link an SD card folder to a tape by presenting it to the reader. After that Wi-Fi switches off and everything plays locally. New tapes need no computer and no reflashing, which seems like the smartest part of the whole design.
One open question remains: the DAC kept cutting out on the speaker above 50% volume, and the cause is still unknown, so the workaround routes audio through the external amplifier. Simultaneous button presses also go undetected, a trade-off the maker accepted.
Project by Nvkv Makes. Watch it on their YouTube channel: