Hey od1, since OFF is taking care of twebbjr and his PWM boards, I've got something for you showing how your PQ controller works the Bertea coils.
Power comes to the controller at the A terminal, then goes to the micro switch (neutral switch on drawing) that's operated by a cam on the side of the controller. When you move the controller in either direction, it operates the switch, which sends power to the C terminal (which goes to the dump valve), and also sends voltage through two resistors to the B and D terminals, and finally to the coil. Since the valve coil has equal postive voltage from either side, and no ground at this point, the coil does not react to move the valve. Back at the controller is the 100 ohm potentiometer which connects between the wires going to B and D terminals. In lever neutral, the pot is centered, making equal resistance to the B and D wires, and the sweep (the arrow coming from the F terminal) inside the pot connects to ground. So you have equal voltage going through the resistors to the coil, and the voltage is being reduced by the resistor in the pot going to ground, everything is balanced. Now, move the controller full stroke to CW rotation. That makes the sweep (arrow) go fully to one side. Now the voltage on B increases because the ground F has moved farther away from it via the pot resistor change, this increases voltage on the B wire going to coil. Likewise, the D wire has a more direct path to ground F because the sweep has moved closer to the D wire and decreased the resistance path. Now you have voltage going to one side of the coil winding and a ground coming back from coil winding which causes valve to shift.
View attachment 49903