LDRs

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tortugaranger

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LDRs
« on: 18 Jun 2014, 04:04 pm »
I've hesitated to write this post because it's not my style to get into controversial topics on an audio forum. However, one Richard Dunn has taken it upon himself to post alarming info about LDRs on this and several other audio forums so I thought it appropriate to provide some clarity.

First, Richard Dunn is a Brit who runs a small audio firm in the UK which also markets a passive preamp product. I know nothing more than that about his company or his products. However, Richard is quite perturbed about LDRs and is making outrageous claims on several audio forums about LDRs being unsafe at any speed etc. At least one audio forum has banned Richard entirely for his inflammatory scaremongering and belligerent attitude. On the face of it, he's conflicted but I've notice he doesn't mention that in his posts.

Audio LDRs are a specialized subset of photoresistors. Photoresistors have been around for decades. I quote from Wikipedia.. "Photoresistors come in many types. Inexpensive cadmium sulphide cells can be found in many consumer items such as camera light meters, street lights, clock radios, alarm devices, night lights, outdoor clocks, solar street lamps and solar road studs, etc." 

Two points warrant highlighting here. First, photoresistors are quite common and used for many things including consumer, commercial and industrial. There's a very good chance you have one or more in your home, where you shop and where you work. Secondly, photoresistors are made with Cadmium Sulphide (CdS) and Cadmium is widely recognized as a toxic substance. You don't want to eat it and you don't want to breath fumes from it when it burns. You don't want to breath fumes from gasoline or drink it either because it's toxic. You get the point.

The CdS in photoresistors is laid down as a thin film and is considered a type of solid semiconductor. They are sealed. LDRs are also sealed. In fact, LDRs are fully encapsulated in a plastic case together with an LED light source. They aren't volatile. They aren't under pressure. They don't leak or spew cadmium. Handling LDRs is safe. They are manufactured and sold by the thousands. The ones we use are manufactured by a company in Canada. You can legally buy them from supplies all over the world...including within the EU. Read on.

RoHS directives were developed by the European Union (EU) to prohibit certain materials in electronics products sold/imported in/to the EU. Cadmium is one of those prohibited substances as is lead. Exemptions are granted under RoHS when there aren't any practical alternative materials. As far as I know, there are no suitable non-cadmium based alternative materials for photoresistors. The EU recognized this and thus granted an RoHS exemption for LDRs used in audio applications. I was made aware within the past week that this exemption expired at the end of 2013. I, along with Chris Daly who also produces/sells an LDR based audio preamp, are endeavoring to ascertain the status of extending this exemption. The way EU exemptions work is exemptions are never permanent. They have a finite life of a few years and then have to be renewed if, in the interim, no suitable alternative substitute material have been found. To my knowledge, none has for photoresistors.

As a matter of course, all of our components are RoHS compliant with the now apparent exception of the LDRs. Plus we use only lead free solder.

In light of this information, Tortuga Audio will likely have to stop selling any LDR based products into EU member countries until such time as the exemption status of LDRs can either be favorably clarified or reestablished.

There are no prohibitions to the use of photoresistors, including LDRs, outside of the EU. We will continue to sell to the world market outside of the EU.

To underscore the irony of all this, solar power is widely supported throughout the EU and many member countries provide substantial subsidies for placing solar panels on commercial and residential rooftops not to mention the thousands of acres of farmland with utility scale solar installations. Several thousand megawatts of solar capacity in the EU use a particular type of thin-film solar panel manufactured by the US based company First Solar. What's the key ingredient of these panels? Cadmium. And in the case of solar panels, there is most definitely a viable alternative material to cadmium. It's called silicon. So it goes.

konut

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Re: LDRs
« Reply #1 on: 18 Jun 2014, 04:58 pm »
Mr. Dunn might want to alert this UK company to the dangers.

http://www.jprelec.co.uk/store.asp/c=1495/Miniature-Low-Cost-LDR

tortugaranger

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Re: LDRs
« Reply #2 on: 18 Jun 2014, 06:33 pm »
Mr. Dunn might want to alert this UK company to the dangers.
http://www.jprelec.co.uk/store.asp/c=1495/Miniature-Low-Cost-LDR

This further underscores the bizarre nature of this LDR issue within the EU. You can manufacture and sell LDRs within the EU but apparently you aren't allowed to make any finished electronic products with them for sale.

Presumably, one could sell products into the EU without any LDRs installed. The customer could then buy the proper LDRs locally and install them. While living in a house covered with solar panels full of cadmium subsidized by the government.

kernelbob

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Re: LDRs
« Reply #3 on: 18 Jun 2014, 07:20 pm »
Since one of the features of the Tortuga LDR controllers is that the LDR's themselves are plug-in units, could you sell the finished controllers sans LDR's and then work out a licensing agreement with an EU manufacturer to build the LDR plug-in units and independently sell those to the EU customers.  Alternatively, you could specify the plug-in units as destined for solar cell arrays.  I'm sure there's an exemption for that noble goal.

tortugaranger

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Some Perspective on Working with LDRs
« Reply #4 on: 19 Jun 2014, 01:39 pm »
1/ they are impracticable for stereo use as they cannot make matching pair.
2/ if you do spend loads of time matching pairs then they drift with age and cock it all up again
3/ they are prone to failure

These 3 points were mentioned on another audio forum as good reasons to avoid LDRs. Since I've personally gone through several LDR design iterations, I thought I'd share my perspective on working with LDRs.

In brief, designing with LDRs is a PITA. There's considerable variability between each individual LDR even of the same make/model. They are highly nonlinear especially over a wider resistance range. Given a choice, it's a rare bird that would willingly choose to work with highly variable nonlinear components in audio equipment design. So why do it? Because it's worth it if you're seeking the best possible audio experience. If you've spent some time around LDR preamps you get the joke pretty quickly. For example, I just had a customer tell me he's selling his $10k tube preamp after auditioning our LDR passive.

As with all analog components, LDRs will drift. LDRs are actually 2 analog components (photoresistor & LED) in an integral package. Most drift just a little. Some quite a lot. If you start with a decently matched set, a little drift isn't a big deal, especially if they all more or less drift similarly. Iv'e had an LDR preamp unit running for several years with no discernible drift that matters. But as I've found out, you can't count on that.

The first version of our LDR passive pre-amp design was entirely dependent on starting with matched sets of LDRs. We had to characterize every LDR over the full resistance range we needed. These tests results went into a database. We'd test 50-100 LDRs at a time. Then we would take that data and run it through a sorting algorithm to select the 4 or 8 best matched LDRs and use those in our next build. A lot of effort went into test rigs, data acquisition, and post-test data processing. We had to store each tested LDR with its own ID tag. Did I mention PITA?

In our second generation design, we still tested each LDR but applied a very different approach where we no longer needed perfectly matched LDRs. Instead, we simply picked pairs of test data points from each LDR that yielded the necessary dB attenuation setting for each volume step for each channel and placed those settings into a table used to drive each LDR at each volume step. Of course this was only possible because our design utilizes a software based digital microcontroller that drives the analog circuitry which regulates each individual LDR. But even with this approach, we had to custom test and calibrate each pre-amp build and store the resulting test data in our IT system. If any software changes needed to made to a customer's unit we had to utilize that original test data. If the LDRs drifted too much, the unit would need to be sent back for retesting and recalibration. This didn't happen very often but once in a while is frankly once too often.

With our third and most recent generation design ("V2"), we got ambitious and made the leap to self-contained auto-calibration where the preamp continuously recalibrates each LDR against a programmed dB attenuation schedule. No pre-matching or testing. Just plug in 4 LDRs and less than 10 minutes later it's ready to go. If one LDR happens to be too far out of spec to calibrate properly or just fails, you pop it out and plug in a replacement, wait 10 minutes and you're back in business. This is a more complex design, involves 12 bit DACs and ADCs, and consequently costs more, but it's completely software driven and the software can be updated via a USB port and a PC. We plan on selling high end finished units and want our customers to know they're getting a great long-term value.

To sum it up, I generally agree with the first 2 points but they can be successfully mitigated if not totally overcome. It's called engineering.

On the last point, I have to disagree. My own experience suggests maybe 1% of the LDRs we use are prone to infant mortality and there are ways of culling those out. The rest will likely live for several 10's of thousands of hours. Kind of like tubes only better.

Cheers,  :thumb:
Morten

tortugaranger

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Update on the EU Position Regarding RoHS & LDRs
« Reply #5 on: 19 Jun 2014, 06:44 pm »
I've been coordinating with Chris Daly of Stereo Coffee who also builds/sells an LDR based DIY preamp board. We have clear common interest in supporting a favorable resolution to the ability to sell products containing LDRs into the EU. What follows is an update that Chris recently posted on DIYAudio in response to a direct inquiry to the EU on the subject.

Based on the timely response from the EU it would appear that we have been cleared for the continued use of photoresistors for analogue optocouplers for sale into the EU although some confusion remains given that the specific exemption for LDRs did run out at the end of 2013. It appears that expiration notwithstanding, that by virtue of a directive that became effective in January, 2013  that LDRs are allowed by virtue of there still being no other substitute materials for the cadmium sulphide presently used in their construction.

What follows here is the EU's response letter text plus some additional commentary by Chris.

_______________________________
Dear Mr Daly,

Thank you for your message.

The Commission Directive 2012/51/EU has enabled the use of cadmium in photoresistors for analogue optocouplers as an exemption from the ROHS directive. Therefore, indeed, the use of cadmium in photoresistors for analogue optocouplers is currently allowed as there are no other substitutes. We draw your attention in this context to the recitals of the Directive:
http://eur-lex.europa.eu/legal-conte...LEX:32012L0051

This new delegated Directive is based on the Recast of the RoHS Directive which entered into force in January 2013. The information relating to the recast of this Directive with the comments submitted during the public consultation is available on the following website of the Directorate-General for the Environment:
http://ec.europa.eu/environment/wast...e/index_en.htm

If you wish to voice your opinion on waste management issues and changes to the EU legislation, we invite you to consult the public consultations webpage on DG Environment:
Consultations - Environment - European Commission

We hope you find this information useful. Please contact us again if you have other questions.

With kind regards,
EUROPE DIRECT Contact Centre
EUROPA ? EU website | Choose your language | Choisir une langue | Wählen Sie eine Sprache - your shortcut to the EU!
_______________________

Chris's commentary....

______________________

A further letter addressed to the National Measurement Office UK asking as to any restriction applying to and relying on ROHS directives will be provided to this forum when it becomes available. It is likely in a similar manner to the EU reply that it will be found that there is no restriction to photoresistors for analogue optocouplers as there is currently no replacement or equivalent product available. If anything changes we at Stereo Coffee will be pleased to let you know. Are LDR pres the ultimate passive? - Page 11 contains further discussion.

Common sense applies to LDR's don't chew or smoke your LDR's. Further information discussing the encapsulated casings is at the above forum, which are entirely safe if used as supplied in our kits.

If you choose to shatter the casings scrape back the lens cover and expose yourself to the resistive coating that is an entirely different matter, as is the disassembly of camera light meters, street lights, clock radios, alarm devices, night lights, outdoor clocks, solar street lamps and solar road studs and high powered loudspeaker voice coils, etc also containing cadmium sulphide.

tortugaranger

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Re: LDRs
« Reply #6 on: 1 Jul 2014, 01:08 pm »
Chris Daly has received an unambiguous response from UK authorities wherein the use of LDRs in kit products is acceptable under UK law regarding ROHS compliance notwithstanding the fact that LDRs are not, in and of themselves, ROHS compliant electronic components due to their cadmium sulfide content.

This affirmative response, together with an earlier affirmative response from EU authorities on this same topic, makes it reasonably clear that products containing LDRs are acceptable under ROHS by virtue of the fact that there is currently no acceptable alternative material to cadmium sulfide in photoresistors.

The fact that a specific EU exemption for analog audio optocouplers  (photoresisotrs) expired at the end of 2013 as a matter of course does not negate the application of this overarching policy.

+1 for rational government policy.

Carry on.

xieqiao

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Re: LDRs
« Reply #7 on: 16 Mar 2022, 12:00 am »
 I hear that the software can be updated via a USB port and a PC, but there doesn't seem to be a download link on the official website for firmware update.

tortugaranger

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Firmware Updating
« Reply #8 on: 16 Mar 2022, 01:48 pm »

I've moved this post into its own topic.

I hear that the software can be updated via a USB port and a PC, but there doesn't seem to be a download link on the official website for firmware update.