/diy/ - Do It Yourself

>>2671647
idk, some old dutch site explained it but I lost the link and it's probably dead now due to linkrot. It's probably a common circuit

Here's what I remember. R2 and R4 are multiturn variable resistors and need to be fine tuned. IIRC R4 controls the steepness of the log/exp curve, and R2 controls the net offset.
You also need to figure out a ~4 component TEMPCO resistor network to substitute R2 and R3, to offset the +3300ppm/C temperature variation of Vbe.
Thermal coupling isn't too hard, just sandwich the tempco between the BJTs and cook some shrinkwrap around them.