[posted] RCA 118 "tombstone" MP3 player


Well-known member
I helped a friend "restore" a 1938 Zenith floor-standing radio, changing it into an MP3 player. We collected old radio broadcasts ("Whistler", "Shadow", "Grand Ole Opry", "Burns and Allen", "War of the Worlds", etc) and separated the content into folders. I use a Teensy to read the capacitance of the tuner to select a folder on the SD card, then randomly choose an MP3 file to play within that folder. I use the audio library to inject hiss in between "stations" and other special effects.
The project turned out so well that I wanted one for myself, but much smaller. I purchased a beat-up RCA 118 radio ( https://radioatticarchives.com/radio.htm?radio=11343 ) and had my friend build a new case. We chopped down the chassis so the entire radio is about a 12" cube. I use one band for the old historical programs and another for modern music. On the modern-music band I have one "station" that is random-play across everything in the band.

Some Photos:

Cut-down chassis

Chassis in new case

New electronics

Completed "radio"
RCA_finished.jpg RCA_finished_front-thumb.jpg
First knob on the left is power/volume control.
Next knob is the band selector (two bands, as indicated on the dial. Top arch is one band, bottom arch is the other.
Next knob is tuning.
The Knob on the right was tone control on the original RCA 118. It is now a forward/back "bump" button to select a different MP3 file.
The blue circuit board is a 20 watt class D audio amplifier, https://www.adafruit.com/product/1752

A 12v supply is hidden in the chassis and plugs into the audio amplifier. I drop the 12v to 5v with a switching regulator to power the Teensy.
The dial lights are now LEDs, I found 12v drop-in replacements for the bayonet style filament bulbs.
The small perfboard hot-glued to the back of the dial has two orange LEDs. I use them as a tuning indicator. When both are off your're centered on a station. As the tuning drifts, one LED gets brighter indicating the direction to turn the dial. The brightness of the LED also indicates how much hiss is being added to the audio.

Oh, the cable dangling under the Teensy is a USB extension cable. It's connected to the Teensy. I use it to reprogram the teensy without having to remove the circuit board.
I literally have been working on the same concept for playing audio! I just shifted to using a Teensy 4 and audio board after struggling to do the audio mixing with a Raspberry Pi.

One thing I’ve got is a sort of randomizer approach where each folder is randomly assigned a frequency, so you have to discover them by tuning. Once set the frequencies persist. Just was experimenting last night with the bitcrusher filter to distort the sound as you get closer to the sweet spot for tuning. I allow stations to be close enough to overlap a bit, but spaced such that each one has a sweet spot where it is just a single station.

I’ve considered the idea of having audio from real radio stations also in the mix as well so that I could have it not just be preset audio. I’m thinking a Software Defined Radio would work for this.
I re-compiled the code using Teensyduino 1.54 and it works great! I have a 64 GB SD card installed now.
I've added an FRAM chip (FM25V20A-PG) to use for shuffle-play. I'm storing 32-bit hashes of the directory (like "A/95" meaning band "A", 950 on the tuning dial) and of the fully-qualified file name ("A/95/Whistler/420627 Notes in the Night.mp3"). By storing both I can easily locate every entry for a directory and clear the entry once everything in that directory has been played.
I have over 400 episodes of "The Whistler" loaded and I've listened to about 100 of them. I've been writing down the episode names I've heard and occasionally moving them to a different directory on the SD card. Now I've moved them back and added their hashes to the FRAM.