Dual Element Optocouplers

[seten]

Whats the dual element? Theres 5 leads, is there just one LED and two photoresistors that share a lead? Whats the benefit of this?

[anotherjim]

I'd hope it emulates a potentiometer. The LDR common is in effect the pot wiper or lug 2, but I don't see how it can with a single common LED. I know some builds call for them but I've never needed one myself - yet.

[idy]

I vote for the first idea. I think that's how the original mutron III worked. 1 led two ldrs. How would you make an "LDPot?" cool idea...

[ElectricDruid]

It's one LED and two photoresistors that share a lead.

A light-variable pot would be a wonderful thing, but that would involve one LDR whose resistance increased at the same rate that the other one's decreased. Not going to happen, unfortunately.

There's still quite a few things you can do with them, despite the "both resistors go in the same direction" and "share a lead" limitations. Light-variable Twin-T filter, for example. Buchla was a fan.

[PRR]

> It's one LED and two photoresistors that share a lead.

One LDR plate with three leads. Like a duplex apartment: three walls make two rental units.

Agree that "potentiometer" with any semi-defined impedance is far beyond LDR technology.

[ElectricDruid]

> It's one LED and two photoresistors that share a lead.

One LDR plate with three leads. Like a duplex apartment: three walls make two rental units.

Ok, same difference! In the UK, perhaps we could call them "semi-detached" LDRs?!

Agree that "potentiometer" with any semi-defined impedance is far beyond LDR technology.

Yeah, that's the killer. Such a shame. We'd have been all over that.

[seten]

Why are they used in the flying pan circuit instead of regular optocouplers?

http://byocelectronics.com/soaringskilletscheme2.pdf

Also, whats wiggling the LED's? Mine are not wiggling Its passing signal that sounds like its stuck in one part of the sweep. No panning either but also still passing clean signal. I'm gonna get all the voltages and make a thread soon but I wanna see if I can figure it out myself first.

[PRR]

> Why are they used in the flying pan circuit instead of regular optocouplers?
> Also, whats wiggling the LED's?

Four LDRs on two LEDs allows working on 9V.

IC1b is a triangle wave oscillator. Does that wiggle? Are there any voltages in it? (There's a bunch of stuff after that to debug, so have low-proof beer/ale handy.)

[seten]

> Why are they used in the flying pan circuit instead of regular optocouplers?
> Also, whats wiggling the LED's?

Four LDRs on two LEDs allows working on 9V.

IC1b is a triangle wave oscillator. Does that wiggle? Are there any voltages in it? (There's a bunch of stuff after that to debug, so have low-proof beer/ale handy.)

Thanks - I'm gonna give it a day or two to cool then I'll get voltages and start a new thread for that. This is definitely above my paygrade.

[anotherjim]

An LDR pot works as a thought experiment. I can even keep only x2 LED wires by fitting x2 LEDs in opposite polarity. In practice, a lot needs to happen to have both LDR halves biased and ranged for the required resistance sweep. A linear pot behaviour is probably beyond it and it would probably only do W or S curves. Good for balance/blend functions maybe.