[sdiy] Bending a Sum

[Paul Perry]

Cheap?
Diode function generator (AKA breakpoint function generator) might be what 
you want.

Basically, it's an amplifier that changes gain when various diodes switch on 
or off,
which is dependant on the input voltage.

an elaborate one here: 
https://www.circuitlab.com/circuit/g2u947/simple-piecewise-linear-approximation-using-diode-function/

But it might be possible to just use a transistor in a feedback loop, as 
here:
http://www.circuitstoday.com/log-amplifier

paul perry Melbourne Australia