Hello yoko1:
Re: No computers in that circuit
My only knowledge about 737 electrical systems comes from PPRUNE. (So I'm a fully-informed expert, right?) In the early days of this thread, back before Ethiopia, there was some discussion about the encoding of angular data produced by AOA sensors. The topic came up as one way to explain a constant difference between values reported by the port and starboard vanes, which is to say, a stuck bit.
Digitization of the AOA reading(s) is, presumably, a first step toward further computer processing. A number of schematics have appeared here on PPRUNE, but they seem to have focussed on the switching logic only, with little detail about where the airplane's own decision-making about MCAS takes place.
I have a very hard time believing that there is no digital computing anywhere in the trim circuit. I am mindful that the military versions of 737 MCAS do have the supplementary g-input that was originally proposed for the civilian MAX. That would have required a whole new layer of analysis and decision-making, and I would be surprised to find that task being by an analogue device. No, there have to be digital computers somewhere in the trim system, as the mechanism by which the airplane controls the trim when it is supposed to.
Perhaps the better question is this: When a pilot presses his yoke trim switch, does that action immediately energize the trim motor with current? Or, instead, is the pilot's action routed as an input to the trim computer, which actually controls the voltage applied to the trim motor? The difference could be fatal if the computer is too busy with other things to process the pilot's command first.
YYZjim