led smoothing

[Kipper4]

Ive got a little project on the breadboard.
using a similar envelope detector to the one used in my gate project last schematic here

some values are differant on my BB project

http://www.diystompboxes.com/smfforum/index.php?topic=113033.40

I'm using the last series LED as part of a vactrol.
the led is for want of a better term is glitching (turning on and off as the notes fade)


Now for the question
Is there a way of smoothing out the LED so it doesnt glitch? and goes from dark to light smoother.
thanks
Rich

[R.G.]

LED light is a reliable indicator of the current through the LED, not all that nonlinear in terms of light intensity per unit current.

You problem translates to "the current through the LED is glitching, turning on and off as the note fades."

I don't know that this is your problem, but it may well be. LED current drops to substantially zero if the voltage across it gets less than the turn on voltage of the LED junction.

The incoming signal on the LED side chain seems to be biased up to one LED voltage high, then there is an LED on the output. The LED on the output is driven on by positive-going signal, and off by negative-going signal. I suspect that the real action on the LED is to have many on/off cycles that your eye integrates to "on" and "off". Not all is lost - the LDR in a vactrol does some integration because it's not fast enough on or off to follow the LED.

But still it will be funny on note tails. This is, by the way, a classical problem in envelope detectors. They all have a trade off in detection speed versus ripple in the output signal. Your single LED setup just makes it more obvious. Maybe worse. Can't tell from just the schemo.

There are some circuit tricks to play, but most of them will drive the complexity of the circuit up.

[Kipper4]

Thanks RG
Lots of room for expansion on this stupid simple circuit.
I'm gonna try tweeking over the next few days and get back to you all.
Cheers

[garcho]

just like audio AC or the PS can be filtered and "smoothed out", envelope detector ripple can be filtered and "smoothed out". the problem, as RG referred to is a classic one; how much detail is in the envelope follower versus how much glitch/ripple gets ironed out.

might not be what you're specifically interested in, but there are some decent op amp envelope detector circuits out there that are neither complicated or huge in terms of tuning the circuit or real estate, with attack/decay controls that can be adjusted to your taste.

[Kipper4]

Thanks Garcho

I've made some progress so I'll start a new thread.
ref ldr sweller