Digital inputs and outputs
All functions are in this single PCB, but I have splitted the Schematics into 3 part for better overview. This part shows the digital inpts and outputs.
Schematic (clock to zoom):
Since the microcontroller has only a limited number of IOs we are using three I2C port expander with 16 IO each, so a total of 48 digital in/out lines. The upper port expander is used for the LEDs, the expander in the middle for LEDs, the push buttons and the rotary band switch and the port expander in the bottom is used the switch the band relais on the filter board as well as various outputs.