generating an lfo

[rhdwave]

Hey all, i've searched through the forum and understand this topic very basically, but was wondering if someone could clarify for me:

When using an ldr, as in the case of a optocoupler how does one generate an lfo.  How does the current going to the led change so as to turn the resistor on and off.  Is this done with some kind of timing mechanism like a 555 opamp or simply a blinking led or is there something i'm really missing here?

Much thanks for any replies!

[varialbender]

The LED/LDR thing is just an interface.
Some circuits are controlled by voltage, and some are controlled by resistance.
Voltage controlled circuits, like a VCO, will let you just hook up the output of the oscillator to it.
The ones working on resistance, like, say, a simple RC filter, don't work like that. You need to have a variable resistor in there. You need the equivalent of replacing the resistor with a pot, and then turning the pot with your hands. Instead of a resistor or pot, you can use an LDR, and it will give a resistance depending on the light it sees. The LED change brightness based on the current it is receiving, thus hooking up an oscillator to it will vary the light and by extension the resistance of the LDR.

The oscillator is another circuit. There are a bunch of them floating around.
http://experimentalistsanonymous.com/archives/
I've used the Simple Dual LFO, and it works pretty well.

Try breadboarding different oscillators and hook them up to LEDs. I wanted to make sure I didn't fry any LEDs, so I always started with huge current-limiting resistors, but that's just my paranoia. After that, you know that hooking that LED up to an LDR should be an easy step, and replacing the two with a optocoupler as well.

Hope this helped.

[gez]

http://www.amazon.com/gp/product/0859343936/sr=8-13/qid=1148506149/ref=sr_1_13/103-1251889-5331852?%5Fencoding=UTF8

Not a bad place to start.

[rhdwave]

Yes that definately helped.  This has been a source of confusion and mystery to me for some time now.  I feel i am finally moving a little into some understanding.  Thanks again for the responses!