October 7th update:
- Analog board UA315 Version 2. Fixed multiple errors in schematics (missing levels conversion for several digital lines), upgraded output amplifier, upgraded analog switch, fine fixes for DC offsets, more filters for DC rails, star grounding, better pairing of layout for DC rails, shielding for isolation of sensitive inputs from outputs (copper ring), shielding of noisy outputs (thick copper ring), single point connects for grounds from multiple DC rails, added multiple test points with jumpers, better attention to silkscreen labels, upgraded transformer with more taps (12 pins).
- Board size reduced to 102x180mm, was 99x199mm (x99 values is to fit into stupid dropdown choice of some other PCB house).
- Ordered the 5 boards batch from Elecrow. Same company, as for first version.
- This board is expected to be final hardware wise. The software is 50% ready and has satisfactory accuracy, readability, speed for 3 of 4 ranges.
I will update how well the V2 build behaved later this month (in October). Couple of parts are still to be ordered from Mouser/Digikey.
The purpose of 1st board is accomplished: to evaluate the noise (bobbing) of measurements. The bobbing is very low, in some ranges the repeatable reading have 0 to 1-2 steps of least significant position (full range is about 10000..20000 counts). The residual noises, interferences are not from any power supply or CPU board, the spikes in bobbing comes only from clocking circuit. This gives me hope that precision of 4-5 digits with minimal bobbing at 4th-5th digit is achievable in final build.