two twenty ma current loops. One Estop sent out , One Interlock sent back, run it off 12 or better 24V isolated, and use these modern 20 mA led current source chips in a 3 pin package. 3 conductors of an ethernet cable are used.
Current mode ignores noise in a club, stage, or cell tower environment. Each projector has two optos, one in, one out. socket the optos, use a 9$ isolated psu module for the hot side of the interlock in the projector, so you have 2 to 4 Kilovolt isolation between interlock / estop and projector electronics. standardize it and make it open source.
Parts cost, dirt cheap...
Reliability, well industry uses 4-20 mA for safety of life controls for a reason. Distance it can go? What half a mile or more...
optos are either on or off, and have protection diodes on them to prevent reverse current. The loop has a series diode and a 150 mA fuse to prevent nasties of noobie wiring.
In theory, you only need 3 wires, to increase simplicity and reliability a bit, I'd use four.
Steve
Last edited by mixedgas; 04-26-2023 at 15:04.
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...