I built the music control head into a hacked-up AM radio chassis. It took probably 20 hours of work over 6 months to complete, a combination of not enough construction time, but also a lot of research and development, choosing guts to match the aesthetic. It's been working fine, exactly as planned and seamlessly as intended.
The AMC front bezel, not shown yet, fits over the LCD perfectly; I replaced the front plexi window (which had the AM radio frequency numbers engraved on it) with clear PETG, masked down with flat black spray paint. I had originally intended status LEDs on the front but that was just faulty thinking; none are needed and would be just distracting.
First, here's the disassembly of the original radio, in preparation of making it into a suitable construct:
For scale, here's the radio out of the car and the computer on the bench behind it (minus a fill panel).
The first thing I do on projects like this is open it up and wash it in a bucket of soapy water. Really. Even if I was going to restore the original electronics I do this. Water won't harm it if you rinse well, shake it off and dry it quickly and thoroughly. It also gets out all the accumulated sticky crud and dust, which will harm it.
This is the radio disassembled into useful (left) and junk (right) parts. I probably won't use all that stuff, and what I do use, beyond the tin box, will be for cosmetics only.
This is the radio station-memory unit. You kiddies out there who didn't grow up with these old mechanical-tuner pushbutton radios in big American cars will be grossed-out and amused. They're really clever memories, they remember the precise position of a rotating shaft that is the actual tuner, using only cheap stamped parts, and do so accurately for 30+ years with no maintenance and lots of abuse. This is from a time when this complex mechanical contraption cost less to make than a transistor! I was going to put microswitches behind each and use them in the MP3 player, but it messed with the interface paradigm, and interfered with the LCD display. I ended up overloading each shaft with a pushbutton.
I was originally going to use my Model 01 Control Engine as the controller, but I'm using and Arduino controller (and have now abandoned my own controller, which made sense in 1998 but no longer does). The Arduino us less than half the size, has built-in USB, you load code via bootloader through the USB connector, and costs $29.
Nearly all the work here was in constructing the controls and getting them to feel right. This is a car, not a desktop. Controls need to provide feedback to your fingers. Operating forces are relatively high with long travels. CLICK. CHUNK. Remember, it's 1970 in here, the wiper switch pulls out 2", the heater control lever pulls a cable that opens a water valve, the fresh air vent is a handle on a door that lets in air. Physicality, not virtuality! Body and brain!
Here's a sloppy outside mockup view, the volume and tuning shafts are in their original place (will be trimmed to length later). I was going to use a 4 line/20 column LCD display, but I didn't like the green color; the entire car is monochrome inside (white and light gray, occasional blue accents) and green really bugged me. I found a black and white 2 line/16 column LCD at Sparkfun, and will make the code fit.
Though it's a bit ugly in there, it's solid. Both the left (volume/pause/play) and right (choose/select) controls are identical, but mirror image left/right. The shaft runs through a bushing, through a brass guide and rests on a heavy action, high-hysteresis momentary Microswitch brand pushbutton switch. The guide has two collars to limit travel. Rotating the shafts has no effect on these switches.
The shafts also have plastic 24-tooth gears attached. These mesh with an identical gear attached to a rotary encoder (quadrature encoder) which lives alongside the rotating shaft. The gear faces are wide enough that they remain meshed when the shaft is pushed.
Here's a closeup of the volume/play/pause control. Note the massive and paranoid cable restraints. Cars are harsh environments, and I want to build this exactly once. You can hardly overdo this stuff. It's all to easy to be casual and get mysterious intermittent problems months later.
Here is the complete working unit. The wiring is not attractive, due mainly to the ugly header plugs required for the Arduino board, but it's solid and would easily survive a fall from 10 feet.
UNDER CONSTRUCTION
American Motors Corporation manufactured automobiles from 1957, when it formed from the merger of Nash and Hudson, until it was sold to Chrysler in 1989. They made solidly reliable economy cars and considering how small they were, a number of historically notable cars under the Rambler and AMC badges, including some very successful performance models like the Rogue, AMX, Javelin, and the first "muscle car", the 1957 Rambler Rebel.