Dual out of sync sine waves?

srynznfyra

New Member

• Jun 20, 2011

• #1

How do I use one or more oscillators (or maybe some other method) to generate dual AC sine waves that are out of sync with each other by 1/2 a wavelength?

Cheers

PS. this is for an LED project - fading a bicolour, common cathode LED between two / three colours.

 

audioguru

Well-Known Member

Most Helpful Member

• Jun 20, 2011

• #2

An inverting opamp will provide a signal that is out-of-phase. Then when the original signal goes positive, the inverted output goes negative.
Or you can bias the circuit so that when the original signal goes up (to brighten an LED) then the inverted signal goes down (to dim an LED).

 

srynznfyra

New Member

• Jun 20, 2011

• #3

OK, I just found a good PDF with lots of examples: https://www.electro-tech-online.com/custompdfs/2011/06/aug_07.pdf

Seems like that's exactly what I need, as if I rectify both outputs, and attach the sine and cosine rectified DC variable currents to each LED (they have a common cathode - tricolour), then I'm predicting it will steadily fade between the two colours.

I'm assuming the capacitors determine the frequency of the oscillator?

 

audioguru

Well-Known Member

Most Helpful Member

• Jun 20, 2011

• #4

The Quadrature Oscillator has sine and cosine outputs which have only 90 degrees of phase shift, not 180 degrees.

The Bubba oscillator can have 180 degrees phase shift.

 

Last edited: Jun 20, 2011

srynznfyra

New Member

• Jun 20, 2011

• #5

Hmm, I was going to go with the bubba anyway as I like quad op amps

Edit: any advice on how to make this an ultra low frequency oscillator? I'm googling of course so I should find the answer soon anyway

 

Last edited: Jun 20, 2011

audioguru

Well-Known Member

Most Helpful Member

• Jun 20, 2011

• #6

For very low frequencies you need opamps that have Jfet very high resistance inputs so the resistor values can be very high. Use metalized plastic film capacitors (they can be as high as 1uF at 63V) because they have no leakage current.