Gracias Steve
Attached here is the block diagram I had in mind to design the circuit whose schematic follows. Since it is a work in progress, I am not going to comment in detail.
The idea of a windows riding the setpoint, seemed to me a simple and good way to avoid integrator windup in the initial stage immediately after a step change in the setpoint. If that proves to be ridiculous, bear with me. I had to literally learn from scratch most of what you see here. I feared diferentiators / integrators as much as interrupts in micros in the past.
Just two names: Walt G. Jung and Ron Mancini. Thanks to them I solved many many doubts.
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Next step is to test the controller as a full PID, including the derivative component.
In case you think I "tuned" this somehow, really I did NOT: I elected a first, random setting for the Kp's pot and then another one for Ki's pot when doing the PI test. Just sheer luck. That's it.
Later I would like to characterize this so as to try it on a different plant to do a predictable tuning or an attempt at least.
Comment: I noticed some unreasonable quick changes in values that suggest maybe the necessity of better decoupling. Sure I have to work on that.
Enjoyed (and enjoying) the journey.