Ill try to answer the questions to the best of my ability.
the nano receives the information (from opengrade >100 or <100) to determine direction up or down… the arduino takes the distance from 100 and sends out a pwm signal thats related… as an example if +100 is up and +2.5v is up(assuming) and the deadband is 2.75v then 101 → 2.75v, 120 → 3.5v, 200 ->4.5v (these numbers are all made up to show the interaction)
The greater the voltage the more hydraulics are applied, in much the same way if you just barely touch the lever it will be slow and the more you push it increases up to the flow rate.
The limits (.5v and 4.5v) represent the extremes of the flow rate, which you set in the monitor.
So, the nano sends the pwm signal via I2C connection to the 4725 which is a 12bit DAC (digital to analog converter), the output of that goes to the lm358 as a booster. Basically the only reason I did this was to use the tractors 5v power to supply the energy to send the signal through 3 ft of wire. I was not sure how much amperage was needed, so I took the weight off of the DAC.
Once hooked up, which has to be done with the engine off or it throws codes, the tractor recognizes touchset control is hooked up. The SCV acts normal and can be used in any way until you do a forwared detent. At which point it reads the signal and controls accordingly. One note, on the 9R I tried forward motion is also needed, I can only assume for safety reasons.
There should be no backfeed as this setup was engineered by deere themselves, its basically like feeding information to a nano on a pin to do another operation.
Timer is no existent, only flow rate.
Im guessing the reason its not digital is this was designed more for a potentiometer to control depth of tillage machines… and like most Deere things it worked so they decided to run with it for other things (igrade, scraper, etc)… Watching the new scrapers Im guessing iso is used, or will be shortly… Im sure it could be used now but it would take someone smarter than I am at ISO.
Hope this clears up the mud a little bit.