[sdiy] SMD LED intensity and lenses

[Tom Wiltshire]

On 25 May 2017, at 17:48, John Speth <john.speth at andrews-cooper.com> wrote:

> PWM is noooisy.....
>  
> So true.  I recently abandoned a design that tried to PWM a vactrol with the intent of "linearizing" response.  PWM noise was everywhere.  It wasn't worth the expense to try to eliminate it.  Another lesson learned.
>  
> JJS

I've had different experiences. Perhaps you have to be careful with PWM, but noise "everywhere"? Nope, not at all. Perhaps it depends how the PWM is generated?

It's a very good fit for vactrols or LEDs. Running a LED from a PWM gives you a good control over the LED brightness without needing some sort of current drive. I've seen circuits where people add an op-amp just to drive an LED, which seems like total overkill.

I've used PWM for LFO output for years now. Running that to a vactrol controlling op-amp gain gives you a dead-simple tremolo circuit. The vactrol's slow LDR response acts to filter the PWM. You can't beat it for features in few parts.

Tom

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