Circuit design so far...(worked up using that Circuit Simulated at
www.falstad.com...love that page... and reworked using LTSpice and generic opamp parts...love that program too)
#1 - The DDS section.
Using an AD9833 DDS chip to make the signal, .65V output. Thru a ~7.8x gain amp, thru a 100K digital pot, AC coupled, adjust the offset with the lower pot, finally into the "power" opamp. Obviously, certain settings off the gain and offset pots will make it clip at one end or the other, but not worried about that. That situation will be avoided in software once I get it built up and characterized (eg. limit the gain with maximum offset one way or the other, and so on...)
Freq's in this case will be limited to about 40Hz up to maybe 100Khz, with the absolute top at 1Mhz mainly limited by the AD9833.
#2 - The ADC input section.
Takes an AC signal, 0 to +/- 15VAC, above or below zero (or centered on zero, whatever), buffers it, attenuates it, mixes it with an offset, then re-amplifies that result to make it stay with the MCU's AD input limits (eg. 0-3.3v or thereabouts). Again, various combinations of input voltages, attenuation (or lack thereof), and offset can cause the final output signal going into the ADC to be out of range, but will be avoided in software once built up and characterized.