Since Chris' model wasn't quite ready at the time, I decided to move on a print a ready made model from thingiverse, scaled to about 16 cm tall, with Eryone yellow PLA, Prusa's galaxy black rings and a few ABS parts, plus the gauge window in Zortrax's Z-GLASS (transwhite with diffusion).

I happened to have a mini bargraph made of subminiature addressable pixels (WS2812 type) on a OSHpark proto PCB with the exact number of lights I needed. At the same time, I had been wanting to write a DMA library for the CFX board (Samd51 based) for the onboard 12 bits ADC and see if I could record sound live on the SD card, without glitches. 

I  had successfully coded already a motion sensor datalogger with high sample rate, exporting a CSV file directly, to measure Tramway vibrations remotely (CFX based too) but it was clearly not the sample rate of sound. I decided to tackle 22.050 kHz for the sampling frequency, way above what's needed for voice but the project can be scaled up for other purpose.

The audio input is made out of a MCP6231 opamp, a simple 50x gain (IIRC) and biasing, presenting the audio signal with a 1.65V bias point to the ADC which is configured in the {0 ; 3.3V} range. The interaction scheme is pretty simple, a top switch triggers either the recording (long press) or the playback. The recording has a 10s timeline mapped to the bargraph filing but you can recording pretty much as long as you want. On playback, the gauge depletes progressively and short presses pause and resume the sound. Since there are only 18 pixels, I used dimming interpolation on each of them to make it look more continuous especially for longer sounds

I envisioned the device as a non politically correct BS detector for meetings, the user would trigger something like a Willem scream each time something helpless is verbalized ^^
But it can also be used in a very poetic way, leaving a message note to your loved one, a reminiscent metaphor for a vocal post-it note, with the nostalgia of tape voicemail and answering machines. I offered it to a fellow researcher - Tom, I haven't forgotten, I'll try to make this lib work for a Metro M0 !

Video quickie