CdS Photocells And RoHs

[TELEFUNKON]

Someone here is not worried.

Andrew

the others can`t rest in peace!

[Unbeliever]

No modern parts that are 'ROHS compliant' have the same 'sound', that's the whole point.  Any 'simulation' of photocell response is unlikely to be viable due to cost / size / workability.

I daresay that that if 'someone' has done a redesign they needn't have used photocells in the first place .... ...

[Brian Marshall]

My real problem is the implementation of it.

A lot of part manufacturers have waited until the last minute to become compliant.

Well it is not even the implementation of it from the government then but how the manufactures have implemented it. I agree they deserve a swift kick for it but at the same time I am not surprised at all. I planned for it. The industry will vote who did well with their sales figures in the end.

Easy to say if you're not selling devices that use parts that don't CURRENTLY have any exemption, eh?

Or one could say if one was seriously looking at selling devices they would have done their research and known about RoHS planning/designing their product to use modern parts the would be RoHS compliant. Someone here is not worried.

Andrew

I think part of the problem with the manufacturers, is that they really could care less about companies that arent buying directly from them, and speding $10K or more per lot.... manufacturers with lots of turn over is where they make their money.

I think in a way they were also trying to make it as a much of a pain as possible because many of them resisted the change.

When i designed the one pedal i have that uses vactrols, cadium wasnt even on my radar screen.  I didnt even think about it.  The only thing that was on my list was lead.  I have found out as well that while some of my inventory that is lead free is not rohs compliant, because it wasnt listed as rohs compliant, just lead free.  luckilly most of that stuff is resistors, and are cheap and easilly replaced.

Also the blue switches from newsensor dont seem to have their paperwork yet.  right now all i have is a personal assurance.

[The Tone God]

No modern parts that are 'ROHS compliant' have the same 'sound', that's the whole point.  Any 'simulation' of photocell response is unlikely to be viable due to cost / size / workability.

The "sound" of something is subjective and out of the scope of this thread so I'll leave that alone. I will say that it is possible to live without photocells. I do think for the vast majority of photocell uses in this field are quite replacable.

Is there a single part that could replace a photocell in all applications ? No. Is it possible to replace photocells in a specific application ? Yes. You have to identify the particular characteristics of the photocell that are the contributing to the function. When you do that you can find other parts/circuits that can meet the design criteria.

I daresay that that if 'someone' has done a redesign they needn't have used photocells in the first place .... ...

I respectfully disagree. If that were the case then why don't we see them being used more often in modern circuits ?

Case in point the Vanishing Point v2.0 has an optocoupler. I decided to design it out for v2.1. I identified the charateristics the opto was providing and redesigned using a simple transistor. In the end it is probably cheaper, easier, more predictable, smaller, will accept a wider range of parts, and if I was producing it could be compliant right now. Yes I still use a photocell on the interface more for the general "safe" interface ability but for example as has been suggested by Mark Hammer it could be replaced using a Dr. Quack style filter which uses a transistor.

Alot of circuits we play with here that have photocells were designed when other replacements may have been to expensive, complex, unavailable, etc. Times and technology have change. It is us, and not just the manufactures in this case, that are kicking and screaming about not wanting to change. In just about every case you can design the part out. It really comes down to the work and know how of the designer meeting the design criteria.

That being said I still think things like tubes. Ges, old ICs, photocells, and more will get exceptions. It will just take time for the paper work to go through to make it official.

Andrew

[The Tone God]

I think part of the problem with the manufacturers, is that they really could care less about companies that arent buying directly from them, and speding $10K or more per lot.... manufacturers with lots of turn over is where they make their money.

I think in a way they were also trying to make it as a much of a pain as possible because many of them resisted the change.

We are small people in the schem of consumer electronics so our voice is sized accordingly. It maybe funny to belive but some compaines don't like to change even if it is for the better so sometimes stronger meassures need to be taken. I don't fault the RoHS one bit for this. It was know to be coming. Yes dealers and product manufactures got jerked around in the deal but as I said you can thank them but using other means not involving them thus they lose sales. I have done just that with certain aspects of forth coming products.

Andrew

[Unbeliever]

The "sound" of something is subjective and out of the scope of this thread so I'll leave that alone.

Photocells respond differently to OTAs - there is *nothing* subjective about that. Engineering 'back' that response from an OTA is possible - but what if you are making a reproduction of something that uses/used photocells? Without the photocells, it is a big step away from being a reproduction, and - if you aren't aware of this - this makes it less likely to be bought by purists, if you are actually trying to sell something and turn a profit.

I agree that for one or few-offs where little or no money is invested in a design or 'sound', it's easy to replace photocells. For the 'rest' (and that might be the minority), it's a matter of tossing away known working PCB layouts, a known 'good' sound and going back to the drawing board to try and engineer a 'sound-alike'. This 'sound-alike' will likely never be quite the same as the original, and can't fail to be more complex. Photocells kick arse because they are small, interface easily (two connections), don't have the current-sensitivity of OTAs ... it's not a matter of being 'stuck in the past', it's simply a matter of choosing the best part for the job. The photocell remains the best choice, IMHO, in many cases.

I'd be interested to hear what Zach would say about this, seeing as his 'seek pedals' use an optocoupler (or at least the Seek-wah did when I peeked inside one a few years back).

[Brian Marshall]

No modern parts that are 'ROHS compliant' have the same 'sound', that's the whole point.  Any 'simulation' of photocell response is unlikely to be viable due to cost / size / workability.

The "sound" of something is subjective and out of the scope of this thread so I'll leave that alone. I will say that it is possible to live without photocells. I do think for the vast majority of photocell uses in this field are quite replacable.

Is there a single part that could replace a photocell in all applications ? No. Is it possible to replace photocells in a specific application ? Yes. You have to identify the particular characteristics of the photocell that are the contributing to the function. When you do that you can find other parts/circuits that can meet the design criteria.

I daresay that that if 'someone' has done a redesign they needn't have used photocells in the first place .... ...

I respectfully disagree. If that were the case then why don't we see them being used more often in modern circuits ?

Case in point the Vanishing Point v2.0 has an optocoupler. I decided to design it out for v2.1. I identified the charateristics the opto was providing and redesigned using a simple transistor. In the end it is probably cheaper, easier, more predictable, smaller, will accept a wider range of parts, and if I was producing it could be compliant right now. Yes I still use a photocell on the interface more for the general "safe" interface ability but for example as has been suggested by Mark Hammer it could be replaced using a Dr. Quack style filter which uses a transistor.

Alot of circuits we play with here that have photocells were designed when other replacements may have been to expensive, complex, unavailable, etc. Times and technology have change. It is us, and not just the manufactures in this case, that are kicking and screaming about not wanting to change. In just about every case you can design the part out. It really comes down to the work and know how of the designer meeting the design criteria.

That being said I still think things like tubes. Ges, old ICs, photocells, and more will get exceptions. It will just take time for the paper work to go through to make it official.

Andrew

When it comes to varying resistance to ground, or some 'known' voltage, transistors can work rather well.

When it comes to varying resistance between two varying voltages, the solution certainly wont be smaller than a vactrol.  I can only think of two possible solutions which would require a lot more parts.

1 Clock cycled pwm switching... you need an oscilator, that can turn a control voltage in to a high frequency PWM signal, and in my experience this is doesnt have nearly the range of a photocell.  It also will make a product subject to FCC rule 15, but i suppose that is irrelivent.

2 a jfet, where the some sort of bias voltage is calculated from the voltage difference across the drain and source, while combining the bias voltage with with a control voltage.  Gawd this would be awful though.  just imagining the component matching problems, and trim pot adjusting.  for true clean operation and response to control voltage its going to take something a lot better than the phase45 setup.... and those are even resistance to a constant voltage.

[The Tone God]

Photocells respond differently to OTAs - there is *nothing* subjective about that.

Agreed but some behavour can be emulated. The question which behavour(s) do you want to emulate.

Engineering 'back' that response from an OTA is possible - but what if you are making a reproduction of something that uses/used photocells? Without the photocells, it is a big step away from being a reproduction, and - if you aren't aware of this - this makes it less likely to be bought by purists, if you are actually trying to sell something and turn a profit.

This is a point where I will diviate from many due to my personal nature of having little interest reproducing previous circuits. From a biz perspective I don't see much "profit" from that but once again that is another thread. What I will say is if it was the case that such circuit would become un-reproducable I would look at the situation as an opportunity to inivate perhaps to beat the competition while they whine about the loss and maybe even improve. Thats just me. I do see your point and concur.

I agree that for one or few-offs where little or no money is invested in a design or 'sound', it's easy to replace photocells.

I'll play devil's advocate for a moment, which I like to do often, and argue that for "little" people it is not easier replace. As the little people, who are doing this as a hobby, are exempt from RoHS they will still be able to use those parts. The little people do not need to source large quantities of parts. The little people can get by finding a few parts somewhere or scrounging in some old circuit for parts.

it's not a matter of being 'stuck in the past', it's simply a matter of choosing the best part for the job. The photocell remains the best choice, IMHO, in many cases.

They are a handy tool which I do use often in my personal stuff and enjoy but time moves on and so does technology. It has happen before and it will happen again. Its a "mother nature" thing. Accept it and love it. The answer is to adapt when necessary which I guess is the reason for this little detour in topic.

When it comes to varying resistance to ground, or some 'known' voltage, transistors can work rather well.

When it comes to varying resistance between two varying voltages, the solution certainly wont be smaller than a vactrol.  I can only think of two possible solutions which would require a lot more parts.

That was just an example I used to show that if one identifies the important parameters one can replace a part sometimes with added improvments. As I said there is no one part that can be dropped in place for a LDR in every application. Your two suggestions are good ones but there are other options to accomplish your needs. You just need to do the work.

Andrew

[Unbeliever]

From a biz perspective I don't see much "profit" from that but once again that is another thread. What I will say is if it was the case that such circuit would become un-reproducable I would look at the situation as an opportunity to inivate perhaps to beat the competition while they whine about the loss and maybe even improve.

The 'profit' comes in two ways:
a) $$$$ for food, rent etc
b) $$$$ to fund other original projects that wouldn't otherwise see the light of day

Maybe it's just my own twisted morals, but I don't see a problems 'funding' cool more original stuff by making reproductions. This isn't aimed at you, certainly, but there's a whole bunch of people claiming to do something 'new' buy making small mods to existing designs ... the whole 'new/old' line is a very blurry one.

As a Buddhist, adopting to change is a necessary thing, but is perhaps the hardest precept to follow. However, I do have a stack of OTAs I intend to put to good use in the near future.... ... I'm trying .....

[Brian Marshall]

That was just an example I used to show that if one identifies the important parameters one can replace a part sometimes with added improvments. As I said there is no one part that can be dropped in place for a LDR in every application. Your two suggestions are good ones but there are other options to accomplish your needs. You just need to do the work.

Andrew

other options... i suppose there could be some type of mosfet solution, but not something i really want to try to think about right now.  most bipolar solutuions wont work because it wont conduct in reverse, im sure there is some elaborate way to linearize them, but its not something i have much intrest in doing with discrete components.

The jfet suggestion is actually not good at all... its actually terrible, especially if you need more than one voltage controled resistor in a circuit, and their properties need to be fairly well matched..  The kind of part matching, and time consuming tuning after the product is already built, probably makes it the worst solution possible.  just imagining the jfet scenerio in my head would require at least 10 parts to replace each photocell, and even then im not sure it would be linear enough.

Anyways, no need to wink at me and say i just need to do the work.    

you say sound subjective and is out of the scope of this thread... was it out of the scope of your circuit redesign.  I have already done plenty of work, and it all has subjective issues that i am not happy with.  When it comes to this business subjective is the only thing that matters.

[The Tone God]

Anyways, no need to wink at me and say i just need to do the work.

The wink was my attempt to reinforce that this point/counterpoint exchange was, atleast on my part, being taking light heartedly or it seems until this point. If you feel that was my attempt to belittle or patronize you I assure you it was not and if an apology is needed then I am sincerely offering it.

you say sound subjective and is out of the scope of this thread... was it out of the scope of your circuit redesign.

To answer your query as I said before I identified the characteristics needed and redesigned based on that criteria. If making those criteria decessions meets your personal definition of "subjective" then be it but it does not fit mine in this particular example.

The topic of "sound" is out of the scope of the thread at hand, which is indicated by the title, so as to avoid the thread from derailing from the OP I chose not to delve into the subject. If it is important enough another thread could be started. I tend to avoid topics from becoming "subjective" because often the thread spirals out of control, sometimes becoming personal for some, with no resolution whereas this thread can have a clear resolution if it remains on topic.

Getting back on topic I restate that RoHS I believe will have little affect on photocells for DIYers which accounts for the vast majority of visitors here. If someone is producing a product using something they are concerned with RoHS about they have three option as I see it.

1. Continue production using the part taking chances.

2. Adapt.

3. Stop production.

Andrew