Thanks Robert -
I already got the voltage supply stuff sorted, that was rather simple. I only didn't use an adjustable LT1117 for the 1.8V supply -- I found a fixed version in my "salvage box" and rather removed the divider network on the HDG PCB. I also did some further testing on the U14 data direction issue and came to a different conclusion: It's got to be an ADuM2402 / 3402 version with two channels in each direction. I came to this result for two reasons: Firstly, it makes no sense to use two different components for U13 and U14 to provide a single additional channel in the Control -> Signal section direction if there's one such channel unused on the other (U14) isolator. Every half-way sane electronics designer (if this doesn't mutually exclude each other
) would use identical parts to keep BOM diversity low and get better prices by sourcing higher quantities of individual components. So in this case, two ADuM2400 / 3400 would have been the way to go (that's what I initially thought without taking a closer look). Secondly, I probed the data direction by injecting a small current (via a multimeter in diode test mode) across the damping network RA8 (fortuantely, there are test pads available). And this test gives clear evidence that the signals on Tp27 and TP28 are driven from the control section.
Yet, when playing with the generator (toy...) I've never seen any activity on the line connected to Tp27 which may explain why your setup works perfectly well with the ADuM3401 isolator.
In general, I agree with what's been said here ragarding the value of the whole gadget - for economic reasons, it's not worth throwing any effort/money after the thing, it's basically crap. With a half-way decent firmware/software package it had some potential but this will most probably never happen. Anyway, I just enjoy playing with it and poking around. If I make a mistake, it wouldn't mean a considerable loss and on the other hand, it works well enough to replace my existing, simple DDS generator. So I simply consider it a toy, no more, no less.
Cheers,
Thomas