DB15 IDC Connector
https://www.digikey.com.au/product-detail/en/cnc-tech/410M0-15-1-00/1175-1813-ND/6024195
15cm 16 way ribbon cable
https://www.digikey.com.au/product-detail/en/assmann-wsw-components/AWG28-16-G-300/AE16G-5-ND/686332
16 Pin 8×2 Header
https://www.digikey.com.au/product-detail/en/on-shore-technology-inc/302-S161/ED10523-ND/2794234
Jumper select ? for Relay vs Button (GPI vs GPO) or have 4 relays, 4 buttons?
3 way Screw Terminals (Relays C, N/C, N/O) x 4
2 way Screw Terminals x 4 (Buttons)
9v ? 5v ? 500mA DC Input (5v Relays)
Transistors x4
Diodes x 4
Resistors
LEDs PSU
LED Off/On per channel?
PCB
DIN Rail enclosure