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Nsl32  Optocuplor
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Old 3rd January 2019, 12:48 PM   #1
birgitay is offline birgitay
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Default Nsl32 Optocuplor

I want to do Nsl 32. Can I make red led and Ldr? In the scheme of blue LEDs and LDR have NSL 32 as well. Red led is a problem
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Old 3rd January 2019, 12:54 PM   #2
Mooly is offline Mooly  United Kingdom
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Nsl32  Optocuplor
Cadmium sulphide photosensitive resistors have poor sensitivity to light wavelengths outside their design range. This means a typical cell designed to have a peak response to yellow/green light will have very poor response to red and blue.

ldr - What Colors or wavelengths are Photoresistors sensitive to? - Electrical Engineering Stack Exchange
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Old 3rd January 2019, 06:06 PM   #3
birgitay is offline birgitay
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datasheet shows blue .. I was angry and did ldr in the little box
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Old 3rd January 2019, 09:10 PM   #4
PRR is offline PRR  United States
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Quote:
Originally Posted by Mooly View Post
Cadmium sulphide photosensitive resistors have poor sensitivity to light wavelengths outside their design range. This means a typical cell designed to have a peak response to yellow/green light will have very poor response to red and blue.
Yes; but an LED nailed to the face of an LDR is "BRIGHT" enough for many purposes. I did a lot of LDRs when LEDs only came in red. Further the historical trend of brighter-every-year works in our favor.

OTOH CdS is falling out of fashion, toxic material. Also became a commodity. Production has shifted from big companies to small shops. Reports are that performance is variable.

Try-and-see becomes the best rule.
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Old 4th January 2019, 08:25 AM   #5
Mooly is offline Mooly  United Kingdom
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True if the light is bright enough and has enough spectral overlap. I'm just not really sure what the OP is trying to ultimately do tbh.
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Old 6th January 2019, 08:06 PM   #6
JMFahey is offline JMFahey  Argentina
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In the old days I also fell for the match-the-spectral-peak trap and used green Leds (CDS peak is yellow-green to the human eye) .. got meh! results.

Surprisingly, most optocouplers (at least all I ever dissected) used RED Leds ... wtf?

Talking about that with a friend, an Engineer specialized in fiber optics and such, told me this:
"human eye has reduced sensitivity to Red wavelengths, so Led makers dope the hell out of them, to radically increase photon-per-mA output so we can actually see them well. ... end result is that photon Tsunami drives CDS cells very well, simply because of sheer abbundance".
So I retorted to high efficiency Red Leds ... instant bliss

But test them yourself: build 2 optocouplers with same batch LDR, one with a high efficiency Red Led , the other with the best "any other colour" you can get.
Pass, say, 10mA through each and measure DCR with a standard multimeter at the CDS end ... lower is better

Please post results.
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Old 6th January 2019, 08:39 PM   #7
leadbelly is offline leadbelly  Canada
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