CdS Photocells

Screw you, RoHS! ; )

You leftists are so depraved you will screw a light bulb socket >:-] ...Jim Thompson

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DEMOCRAT

The Party of Sexual Deviants and Unions Covering for Bad Teachers

Patent US3208022 ????

Cheers

Even a dirty enviro-weenie such as myself finds many of the RoHS regulations absurd and draconian.

There need to be exemptions for a lot more things than there are.

Like audio equipment...

What does that have to do with my post regarding CdS photocells? ...Jim Thompson

Watch out, Jim Thompson wants us to stay on topic now! Jawohl Mein Fuhrer, I shall do zee research...

Could be 10ms give or take quite a lot. Be aware that they have a 'memory effect' which basically means you can't rely on getting the same resistance for the same illumination after a temporary change in illumination.

I remember well the line equaliser design which used vactrols, and the confusion when the settings could not be repeated.

Cheers

Back in the day that slow-response and memory effect was considered a nuisance for audio compressors...now they sell for huge money and it's called "character."

My 50+ year old remembrances of a chip design for automatic headlight dimming for Guide lamp Division of GM were fast attack and gawd-awful slow return to dark resistance.

But current inadequate "datasheets" claim 5ms attack, 10ms decay, which seems grossly wrong. ...Jim Thompson

Digikey is still selling CdS cells. I wonder if they are illegal in Europe.

What about arsenic? As in GaAs?

And do his Googling for him!

Well, the greenies want the level of As in drinking water to be 0 PPT (immeasurable), though it's naturally occurring in much of the world. Look how much more we're putting into (sealed) landfills.

Or Beryllium Oxide in high frequency power resistors.

The last time I used a CdS photocell to control a resistance (actually audio attenuation) I had a pair of the things using the same LED current, using one of the CdS cells as a reference (inside a feedback loop). The tracking between the cells wasn't great (don't recall the numbers), but better than no compensation at all.

Regards, Allan

I'm trying to write a Spice model which, at least, is a close approximation to attack and decay time constants. The manufacturers seem afraid of showing more than a very rudimentary amount of data. ...Jim Thompson

IIRC, CdS photocells (in conjunction with a light bulb) make a dandy variable resistor to electronically attenuate audio.

Yep. I'm trying to Spice behavioral model an LED/CdS Optocoupler product, Silonix NSL-32R3, but the published time constants don't fit with my past experience with such devices. ...Jim Thompson

Maybe different mixes have different time constants, like gold in transistor bases?

I know that just about every cheap tachometer for radio control airplanes uses a CdS cell, even though photodiodes are superior and cheaper.

IIRC datasheets on varactors (or varactols?) have detailed spec on the cds cell inside. I know either newark or element 14 still stock them and list and link to a data sheet