[sdiy] A simpler LED/Optocoupler/Vactrol dimmer

[harrybissell at wowway.com]

Once you have linear control (opamp feedback) you can add
expo, or log circuits before that stage to drive it.

You would ideally want an opamp per LED anyway. If you have only 
a couple of LEDs they couls be in series...

H^) harry




On Thu, 3 Apr 2008 20:02:36 +0100, Julian wrote
> > Put the LED in the feedback loop of an op-amp. Makes it linear.
> 
> Ive been thinking of using vactrols to control some things, and 
> Grant / Harry have just demonstrated how to get a controlled linear 
> response, but what about a controlled antilog response, and a 
> controlled log response?
> 
> Basically i want to use the same value control pot for every vactrol,
>  and have some varying logarithmically between value a and value b,
>  and some varying with a linear response from b to a, some from c to 
> d etc.etc.  I want lots of different resistances and 'tapers' from 
> the same input.
> 
> In truth, i havent really thought about this very far, but its the 
> antilog that seems the problem...
> 
> Julian
> 
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Harry Bissell & Nora Abdullah 4eva