This VicRel clone cartridge open source project is from German Forum64 board (more information available in here: https://www.forum64.de/index.php?thread/40223-gesch%C3%BCtztes-i-o-interface-f%C3%BCr-den-userport-joyport-nein-es-wird-keine-platine-ge/&pageNo=3)
Manual: https://www.manualslib.com/manual/1475462/Commodore-Vic-Relay-Cassette.html (read with care, 1st time I was testing it with my C64, I didnt notice that examples had vic peek values and the corresponding C64 value was mentioned at the end of the manual).
With this you can control 6 output releys and 2 input relays.
