“Serial (ascii) monitor with 9 lines of 28 char.
Baudrate from 2400 up to 256000 baud.
Digital 3.3V or 5V input.
Powered by a single Lithium-Ion battery. (3.7V nominal)
ILI9341 display (here a parallel version is used)
BluePill (or other board with a STM32F103C8)
74HC14 (hex invering schmitt trigger)
3.3V low dropout voltage regulator
rotary encoder (with or without button)
lithium ion battery (e.g. from old telephone)
some capacitors and resistors