[sdiy] A simpler LED/Optocoupler/Vactrol dimmer

[harrybissell at wowway.com]

You can put the LED in the feedback loop of an opamp
(inverting) and drive it with current.  Set the input
resistor for the current you want per volt, for instance

H^) harry



On Wed, 2 Apr 2008 20:38:33 +0000, 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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Harry Bissell & Nora Abdullah 4eva