From: jl@glen--canyon.com   
      
   On Tue, 10 Feb 2026 07:49:22 -0900, Christopher Howard   
    wrote:   
      
   >> 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.   
      
   A simple opamp circuit with some resistors and diodes can have a   
   several-segment approximation to a square root. I did that in a   
   steamship throttle control once and it worked well enough.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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