From: christopher@librehacker.com   
      
   > Standard apprach for low-accuracy approximation is diode-resistor   
   > network.  But such network gets inpractically large if you need   
   > good approximation.   
      
   Thank you. Looking at all the suggestions put forward, it seems like —   
   for my application — that just getting the AD633 might be best choice.   
   My analog computer is short one multiplier for a simulation I wanted to   
   play with, and I wonder if there was some easy trick to get a reasonably   
   accurate square function without getting a decent multiplier. In a lot   
   of basic physics simulations, one has to square velocity to get   
   things like drag or lift forces.   
      
   Line approximation with a resistor-diode has some appeal. Maybe it could   
   be accurate enough for my little educational experiments? I think, to   
   pull it off, I would need to use trim pots — two per segment, for the   
   biasing and the attenuating.   
      
   The schematic from the neurological paper seemed to be a line   
   approximation solution with some of the diodes in the op amp feedback. I   
   didn't try to get the whole research paper so I'm not sure how one would   
   work out the correct resistor values.   
      
   I downloaded the information on the MC1496-D and LM13700. I see the   
   basic idea is that these chips also produce products of signals, but   
   beyond that I can't make any intelligent comments at present. My analog   
   computer is usually dealing with signals in the range of a few hundred   
   Hz up to a few kHz. I am curious if maybe something could be done with   
   the gain control pin on the LM386 chip (I have quite a few of those). It   
   looks like, using a series RC network, that the gain can be set anywhere   
   from 20 to 200.   
      
   --   
   Christopher Howard   
      
   --- SoupGate-Win32 v1.05   
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