I am looking for an AGC (Automatic Gain Control) which outputs not only the normal output but also another output which tells you what gain it is using. I need this for an automatic voltage meter I am building; it doesn't have to be an AGC just some kind of device which changes its output voltage if the input voltage is out of the scale I am measuring, but tells me the gain so I can know the input voltage. I was thinking maybe comparators that if I pass a certain voltage it changes a voltage divider.
The approach that springs to mind is to input a small high frequency sine on top of your regular input signal, band pass to find out how big it is, and then high pass to get rid of it. It means you can't low pass at your amplifier, but it's fairly straightforward.