Yes I agree. My long term plan with the software is to write a C++ class called "DAC" where you send it a voltage. The class hides the way the DAC works. I was also thinking like you to treat this as two DACs where you use one for fine tuning and the other to make a course adjustment to place the desired voltage in the center of the fine adjustment DAC's range. And not treat this like a 16-bit DAC. This moves the discontinuity out to some place where it will never be used. But this is low on my list because by luck I not operating near the transition.
But as I wrote before I first need a good way to test this and get the test data into a computer. On Fri, Apr 11, 2014 at 9:20 PM, Hal Murray <[email protected]> wrote: > > [email protected] said: > > My plan was to eventually fix this in software. Using ultra precision > > resisters is not a good fix. I'm using normal 5% 1/4W resisters. > > > I don't think I will get stuck. if a step is to small it will simply > move > > up the next DAC value. The I term in the PID controller will basically > see > > that the current DAC setting is not enough can add more. I is (error * > > time) and given enough time it will push the DAC in the right direction > even > > if the error is very small. > > The way to get in trouble is to have the step size of the big DAC be bigger > than 256 x the step size on the small DAC. That would leave a gap between, > say, 3FF and 400 that you can't get to. > > [I see lots of opportunities to get the words wrong here.] > > If I was doing it, I'd try making the step size on the big DAC be 1/2 of > the > range of the small DAC. The idea is that you don't plan to change the big > DAC. If you need to go up from 3FF, you will end up at, say, 440. That > will > leave you room to go back down without having to change the big DAC. > > Of course, that only works if the active/working range is a fraction of the > total range of the small DAC. > > > > I don't have a good way to test the DAC. My Fluke DMM can't see any > > problems. But eventually I want to add a self test or self calibration > > function. I figure that the OCXO should be a very good voltage meter. > > Using the osc was the first thing that came to my mind. > > You might be able to see it on a scope if you took out the big caps and set > up the software to toggle between two values and flap a pin to trigger on. > > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
