Inverting LFO driving an LED

[soggybag]

I have LFO that drives an LED. I want to invert the signal so that as one LED lights up the other dims.

This came up some time ago. I remember there was a simple idea. Where both LED's ran off the single LFO.

I found this thread. It appears the images are missing so some of the ideas are a little cryptic.
http://www.diystompboxes.com/smfforum/index.php?topic=33221.0

[slacker]

Here's a couple of ways of doing it, they both assume the output of the LFO is centred roughly around half the supply voltage.



The first one is probably what you want, as one LED gets brighter the other one gets darker. You might have to play about with the resistor values to get an even sweep.
The second one gives your LFO two outputs that are out of phase with each other, that you can use to drive whatever you like.

[soggybag]

That is exactly what I was looking for, thanks Slacker!

[puretube]

not "cryptic", and not "missing"...

just lost in the several forum transitions... :

http://www.diystompboxes.com/smfforum/index.php?topic=29374

[soggybag]

PureTube that is a work of art!

[Processaurus]

You'd probably know this, but that first one only works with a low impedance source, like the output of an opamp in a typical 2 opamp lfo, LEDs will load some less robust LFOs down and make them latch up.  Also worth checking current rating on your opamps, I do know LM358's are happy sourcing and sinking enough current to light LEDs.

[mac]

I had problems with the above solutions, mainly you could not balance the leds.
I modified the Phozer2 LFO at ROG, added a second trimmer and the led to vcc.

mac

[darron]

slacker is on the mark, especially about the half voltage. you may need to play with the resistor values to match it up correctly. different leds will behave differently too, so get ones that match.

there's a link here with a sample schematic that i have tried that works (although i think the values i used were totally different, the concept is there):
http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm#eyes.gif

it has the emitter-follower on it too. go to 'fading red eyes' and look at the bottom schematic.

here's a video i made of it in action:
link