Half Sine wave 90degrees out of phase...or something. Help

[snarblinge]

Ok so this started as "replace the foot on the wah with a circuit to do it" and I thought i could plan a building block which could be fun in a bunch of pedals.

decided a simple lfo may not give the nicest sweep, so built a xr2206 based Sine generator.This I  linked to two leds which i planned to attach to LDRs or replace with optocouplers. of course then i realised that I have a dead patch in my sweep each LED ramps up and down and then stays off while the other ramps up/down. i was planning to chuck a phase splitter on the end but then i will just have two going at the same time and still have the same dead patch issue???

really i need two half sine waves 90degrees out of phase. how do I best achieve this?

thanks all

[Keppy]

Google "quadrature oscillator." This is a type of phase shift oscillator that relies on four stages of phase shift to produce a sine wave. Since there are four stages, each one contributes 90 degrees of phase shift. Using the outputs of adjacent stages should yield sine waves 90 degrees apart. After that, half-wave rectify each signal with a diode.

EDIT: Aaargh, all the oscillators I've been looking at are running together in my head. Quadrature is the one you want, but my explanation was off. I was mixing descriptions of the quadrature and Bubba oscillators into some magical creature that does not exist.

[snarblinge]

thanks, i knew something had to be out there. re-googling asap

[moosapotamus]

I was looking for a quadrature LFO some time ago but, at the time, all the quadrature oscillator schemes I could find seemed to only run at higher/audio frequencies. Interested to see what you come up with.

~ Charlie

[oldschoolanalog]

Sift through this. Maybe it will give you some ideas:
http://www.diystompboxes.com/smfforum/index.php?topic=72676.0

[Keppy]

You can increase the R & C values to slow down an oscillator. I built the sine wave oscillator from the LM13700 datasheet and it works well from several kHz down to <1Hz with the cap values I chose.

[snarblinge]

Ok update, found the parts count was going to be to high to do exactly what i wanted. so have decided to dive into digital land.

ordered an arduino kit, as I have a friend who has built a robotic arm and has a handle on it and thought this would be a good starting point.

originally was going to run a pot into it, and output to LED/LDRs to recreate the pot.

have since discovered digital pots and seems this is a much more sensible way of going. the pot interfacing with the arduino is easy, the digital pot controlled by arduino looks do-able. just reading all I can to try and figure out how to use the pot to set frequency/speed of the changes. it seems this isn't something arduino nerds want to do. they just want to make LEDs blink and fade..... 

[moosapotamus]

Sift through this. Maybe it will give you some ideas:
http://www.diystompboxes.com/smfforum/index.php?topic=72676.0

Including R.G.'s original suggestion to go with a uC.
I went part of the way down that road back then. Should probably get back to it and follow snarblinge's lead.
But that thread is a great read. Thanks for bringing it up.

~ Charlie

[frequencycentral]

The 3rd way might be to use a PT2399 to process an LFO, thereby allowing you to define how far out of phase the input is with respect to the output. Would require a bit of biasing and attenuating of the input, and re-biasing and amplification of the output.