LFOs and Vactrols- depth control

[spectraljulian]

I've been trying to add this LFO into one of my designs, and it is a design that will work with a changing resistance but not a changing voltage. 

So that's OK. . . I'll wire a vactrol right? 

I wired up a LED and put a depth pot fading the output to ground before it. 

I then realized though that with the depth control wired up this way, decreasing depth also increases the lowest point of resistance since light = less resistance.

So basically I need to rethink my depth control.  I want to make it so that as I turn the depth pot the LED's darkest point gets brighter. 

Any ideas? 

[daverdave]

You should note that the lfo you are using, like most 9V circuits, is single supply. That's why it has a voltage divider circuit to create a 'virtual ground point' or common voltage of 4.5V, this IS the ground for the circuit, so you could look at it as +4.5V and -4.5V.

I'd connect the bottom lug (lug-1 I'm guessing) of your depth pot to +4.5V, which is your virtual ground, it will level out at half voltage then, instead of being pulled to ground.

[spectraljulian]

Colin recommended that and when I do that the LED just stops blinking and depth purely controls brightness. 

With it fading the output to ground once I turn the depth to be near maximum brightness it just stops pulsing until I turn the brightness down a bit. 

Measuring the output of the LFO, it goes between 1.9 and 6.7 volts.  I'm thinking when I have the depth set to maximum that the LED always has enough power to be fully lit and thus doesn't fluctuate.  I'm sure I should have a limiting resistor there in my final design. 



But my problem isn't that the depth control doesn't work, it's that it works backwards, because I will be using one of these guys:

http://www.smallbearelec.com/Detail.bok?no=711

So with my depth decreasing brightness I'm also increasing the minimum resistance of the LDR. I want my depth to control the maximum resistance without changing the minimum resistance. 

I'm currently working around with wiring the LED differently. . . putting the negative lead to 4.5V instead of ground, running off the 9vs for an inverted output. . . they're all giving me results less desirable than what I have where I have depth pot fading to ground with the LED also connected to ground.