The concept:
Read keystrokes over serial, parse them into their binary ASCII values, and light up corresponding LEDs.
The Build:
Arduino ProMicro has 8 LEDs connected to 8 pins (2-9) through 10K current limiting resistors, soldered onto a perf board. The whole thing is permanently embedded into a 1-piece 3D printed enclosure by pausing the print, placing the circuit inside, printing the top over it, permanently fixing the circuit inside the housing, printed in transparent PETG.
10k is too much