Today I’ve finished and tested front panel PCB.
You may find one noticable feature on this board: I’ve used MEC 3FTL buttons instead of widely available and cheap B3F-like tact switches. Theese switches are designed to embed 3mm LEDs and have longer travel distance.
Panel has total of 13 inputs distributed between 2 IDC sockets. It’s connected to control board with two ribbon cables. Backlit is powered by 12V PWM controlled signal and is connected to control board with separate 2-wire cable.
In fact it’s not control board. It contains three MCP23S17 modules intended to be connected to MCP’s Arduino board.
MCP23S17 allows to connect up to 8 devices on single SPI line. Each device has 3 pins to set it’s address. Each EFIS can be configured as captain’s or 1st officer’s with DIP switches, that are used to set address of MCP23S17. That’s how it works.
Board installed on the EFIS module: