[sdiy] Simple circuit challenge: |a-b|

[mskala at northcoastsynthesis.com]

On Thu, 21 Mar 2024, Rutger Vlek via Synth-diy wrote:
> rectified. The total is 3 opamps, 2 diodes and 9 resistors. As I need to
> repeat the circuit many times in the final application, I'm wondering: is
> there anything simpler that can do this?

I'm not sure it's really going to make an important difference, but you
could use a single op amp full-wave rectifier to bring the component count
for "absolute value of difference" down to two op amps, with associated
reduction in support components.  I used it in my Coiler VCF, and the
circuit is described on page 35 of the manual here:
   https://northcoastsynthesis.com/products/msk-009-coiler-vcf.html

I've seen it in a few places online, usually attributed to "Tompkins,
W.J., and J.G. Webster (eds.), Interfacing Sensors to the IBM PC.
Prentice-Hall, 1988," but I haven't actually seen the original print
publication.

-- 
Matthew Skala
North Coast Synthesis Ltd.