[sdiy] A simpler LED/Optocoupler/Vactrol dimmer

[Grant Richter]

Put the LED in the feedback loop of an op-amp. Makes it linear.

On Apr 2, 2008, at 3:38 PM, Justin Owen wrote:

> Hello,
>
> Thought I'd post this here because I know a few of you use LDRs/ 
> Vactrols in your projects.
>
> I've been using the H11F3 optocoupler as a modulation destination/ 
> controller. Very cool little IC - but I've still got the age old  
> problem that controlling the brightness of the internal LED with a  
> regular pot gives me a very uneven taper. i.e. approximately 90% of  
> the taper gives a very small increase in brightness and the last  
> 10% or so jumps right up - which doesn't make for a very even  
> control curve.
>
> I know the standard way of improving this is to use PWM to control  
> the brightness - and the couple of circuits I've tried have  
> definitely been an improvement...
>
> ...but - I was wondering if there was simpler way - somewhere  
> between just a pot and a full-blown PWM circuit? (On this project  
> I've got the equivalent of 11 LEDs to control - so that's a lot of  
> extra components).
>
> I was sure I saw something about adjusting the taper of a pot  
> somewhere - but for the life of me a I can't find it now.
>
> Any clues would be most appreciated.
>
> Thanks much - J
>
>
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