Inverters/NOT gate without transistors

The elevators in my building were originally installed in 1975. Some time around 2005 before I lived here they got a “brain transplant” and the controller up in the machinery room is now a couple of circuit cards and a bunch of status LEDs.

Still sitting in the room is an electrical cabinet about 6’ tall, 3+ feet wide and about 1 foot deep. When you open the door it’s a wall of relay sockets, each about 2"x1.5". There’s roughly 700 of those sockets.

The wiring plane is on the back side against the wall and the damn thing weighs hundreds of pounds and can’t practically be moved. Which is why it’s still sitting there.

All the relays themselves were pulled from their sockets. Probably to be used as spare parts for other older elevators the company serviced.

By coincidence I was looking at this relic just last week.

1975 was two years before I took the class, so I guess it wasn’t too far back in the day. State machines (the prof called them “finite state automata”) built with electromechanical parts.

How about Fluidic logic?

You are correct. Sorry, brain freeze.

Wow, that’s really cool.

~Max

How does that work?

Veeeeeeery slowly.

Anything bimetallic will tend to bend once heated, if the coefficients of expansion of the two materials differ.

Domino stones.

Oh, and the flows of gases in jet engines, for instance.

A mechanical computer using marbles:

Digi-Comp I

And, Dr. Nim:

I had a Dr. Nim. That’s what made me think of marble-based computers x looking for a cite took me to the Digi-Comp.