These are the hardware chips that will be responsible for scanning the potentiometers.
2 x CD4067 16 to 1 Analog Multiplexer
1 x TLC549 8-bit Serial A/D Converter.
The multiplexers will enable the PC to choose 1 of 32 analog inputs for A/D conversation by the TLC549 A/D converter. The endpoints of the potentiometers are tied to +5v and Ground and the center of each are routed to an analog input of the CD4067. The frontpanel program scans through each of the pots and registers any changes, transmitting these as MIDI-CC.
The display part is a standard 20×4 LCD with a yellow backlight connected to the PC with a 4-bit interface enabling the frontpanel program to display any characters or graphic on it.
The display is very easy to interface with thousands of examples on the Internet.
The frontpanel buttons are connected to the standard PC-keyboard scanner resulting in normal keypresses to the frontpanel program.
Here is the complete schematics with the 4 chips and display connected to the parallelport.
The 4th chip is just an 74LS04 Inverter used to extend the adress range for the multiplexers to 5bit linear adress instead of 4bits per chip.
There is actually a bonus using an A/D converter, it converts analog voltage to a MIDI-CC so if we would like to have a CV input, no problem, just connect a jack to one of the multiplexer inputs. It’s that easy.