Deal with Optocouplers & LED/LDR's

[Baran Ismen]

Hi.

I was standing back a little from optical-based circuits due to usage of Vactrol's or LED/LDR combo's, because Vactrol's are unavailable here, there are some opto's like xx817 (no idea about their suitability), and some no name, different sized LDR's (5mm, 11mm).

Now;

I know the working principle of these, but I don't know which values(s) should I consider for any optical layout I want to make. I'm also not familiar with the terminology of it, either. Does the dark or light resistance matter; i.e? Using a correct LDR is a must? Any type of LED would work?

Some enlightenment would be good here, as I want to proceed with DOD 440 initially, then some other optical-based circuits.

Would a pack like this one sufficient for me for general purposes?

[duck_arse]

that pack would just about cover any circuit you could think of. to some extent. is it expensive?

[amptramp]

The DOD440 uses a centre-tapped photoresistive element with single LED driving both elements.  Each side of the photoresistor is in parallel with a 220K resistor, so the dark resistance is probably on the order of 1 megohm with the resistors setting the dominant resistance in the dark state.

Photoresistors are usually specified with a minimum dark resistance, resistance at one footcandle and resistance at 100 footcandles of incandescent light at a 2870 Kelvin temperature (which sets the spectrum as a typical incandescent white).  Usually, red, yellow, green or white LED lighting is effective.

If you plot a log scale of resistance on the vertical axis and a log scale of illumination on the X axis, the resistance vs. illumination curve will be a straight line going down to the right with more illumination resulting in lower resistance.

These are cadmium sulphide devices and since cadmium is one of the three metals (along with lead and mercury) that are prohibited in RoHS specs (reduction of hazardous substances), you will probably not find any new ones being made in Europe.

If you have a DOD440, you can disconnect the device and measure it in dark, 1 footcandle and 100 footcandle illuminations and see if you can characterize the device.  Note that it takes a while for the dark resistance to rise to the value it eventually gets to.  Even if you can't determine the illumination you are testing with, you are looking for matching resistances at low light and high light.  A typical office is lit up to 70 to 100 footcandles and one footcandle is relatively dark.  The kit of photoconductors you have mentioned probably contains usable values although I don't know if this is expensive or not.

[Matthew Sanford]

Hi.

I was standing back a little from optical-based circuits due to usage of Vactrol's or LED/LDR combo's, because Vactrol's are unavailable here, there are some opto's like xx817 (no idea about their suitability), and some no name, different sized LDR's (5mm, 11mm).

Now;

I know the working principle of these, but I don't know which values(s) should I consider for any optical layout I want to make. I'm also not familiar with the terminology of it, either. Does the dark or light resistance matter; i.e? Using a correct LDR is a must? Any type of LED would work?

Some enlightenment would be good here, as I want to proceed with DOD 440 initially, then some other optical-based circuits.

Would a pack like this one sufficient for me for general purposes?

That 175 pack is what I used with 5mm flat top green leds to make vactrols. It seems you want two attached to one led if I read amptramp right on the DOD440. I know with what I made, one LDR taped on the led them wrapped with silicone tape (for plumbing) Like thisI'd get about 400-20m+ ohm range.

Antonis had mentioned the light is brighter on the sides.

[Mark Hammer]

In many instances, the resistance of an LDR, and change in resistance in response to illumination, can be compensated for by adjusting other components.  Keep in mind that we cannot see inside a sealed Vactrol, to know just how bright the LED element is.  All we can do is adjust the current/voltage driving that LED in known ways, and measure the LDR resistance.  You can do that with a home-made LED/LDR combo.  It's handy to have superbright LEDS (i.e., at least 6000mcd rating) since that gives the option of limiting their current to achieve the desired resistance change and range.

Of course, what you can't always alter is the rise/fall time of the LDR.  Some applications, like compressors or noise gates, tend to need a given range of on/off times, but most "plain vanilla" LDRs with a 2M-or-greater dark resistance will have suitable rise/fall times for an EF440.  Make sure that testing for dark resistance doesn't just involve putting your handover it, because light goes through your hand.  Testing dark resistance should involve covering the LDR or LED/LDR assembly with something thick and opaque.

The EF440 s a nice pedal.   made one a while back and rather liked its "vocal" quality.

LEDS can be filed - at least the clear plastic part - to provide flat surfaces for  pressing LDRs up against their side/end and gluing them in place.  It's a good idea to buff those surfaces with very fine emery cloth, after filing, so they are smooth and allow maximum light out.

[PRR]

Would a pack like this one

I get a robot challenge:
"Aşağıda gördüğünüz karakterleri girin
"Üzgünüz, sadece robot olmadığınızdan emin olmalıyız. En iyi sonuçlar için lütfen tarayıcınızın çerezleri kabul ettiğinden emin olun."

But the "challenge" was Roman letters on two diffeent slants so I managed. Why is Amazon being paranoid??

YES, if you can get a hundred+ LDRs for $13, buy it!

[Phend]

$13.. Ouch, bet 2 good beers cost that much.

[Rob Strand]

But the "challenge" was Roman letters on two diffeent slants so I managed. Why is Amazon being paranoid??

Happens a lot to me on Amazon and I hardly go there.

[Matthew Sanford]

Would a pack like this one

I get a robot challenge:
"Aşağıda gördüğünüz karakterleri girin
"Üzgünüz, sadece robot olmadığınızdan emin olmalıyız. En iyi sonuçlar için lütfen tarayıcınızın çerezleri kabul ettiğinden emin olun."

But the "challenge" was Roman letters on two diffeent slants so I managed. Why is Amazon being paranoid??

YES, if you can get a hundred+ LDRs for $13, buy it!

Switched to Turkey on the app for me, took a minute to figure how to get back to the US cause Dave never taught me Turkish (so Dave...). But those are what I got. They have a wider range than what they list, but after learning about footcandles (thanks Ron!) I realize I must've been using metercandles.

[Baran Ismen]

that pack would just about cover any circuit you could think of. to some extent. is it expensive?

It's about 12 bucks when converted to TRY.

[PRR]

Those LDR part numbers in variety packs are available at affordable price on the Asian mega markets and also in the USA.
https://juriedengineering.com/products/gl-series-photoresistor-kit-5-gl5506-5-gl5516-5-gl5528-5-gl5537-5-gl5539-5-gl5549-photo-light-sensitive-resistor-kit-of-30-pieces
Kit of 30 Pieces Juried Engineering $11.49 USD

Ah, Amazon "gl5506-gl5549": 175 pieces for under 12 US bucks:
https://www.amazon.com/Photoresistor-Photosensitive-Resistor-Sensitive-Resistance/dp/B0CQJDZMCY
https://www.amazon.com/Qyebavge-Photosensitive-Resistor-Including-Electronics/dp/B0CRF8KLHG
https://www.amazon.com/Photosensitive-Resistor-175Pcs-GL5506-Electroniccomponents/dp/B0CNTQ22TY

I am not familiar with "GL" series LDRs but I found this data-sheet:
https://www.kth.se/social/files/54ef17dbf27654753f437c56/GL5537.pdf

[Matthew Sanford]

This is the info I'd found on that 175 pack of LDRs. I've mostly used the 5539s, but the go much lower than stated (400R instead of 30-90k)


Xingyheng ldr

The set includes common used 7Values, 25pcs for each Value, total 175pcs.

Feature : --Maximum Voltage--Maximum Power--Operating Temperature--Spectral Peak--Light Resistance (10Lux)--Dark Resistance--Sensitivity--Response Time : rose and Drop

GL5506------100 (VDC)-------90 (mW)----------- -30 ~ +70 ℃------------ 540(nm)----------2~6(kOhm)----------------0.15(MQ / MOhm)-----0.6(min)-----------30 and 40(ms)

GL5516------100 (VDC)-------90 (mW)----------- -30 ~ +70 ℃------------ 540(nm)----------5~10(kOhm)----------------0.2(MQ / MOhm)------0.6(min)-----------30 and 40(ms)

GL5526------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------8~20(kOhm)----------------1.0(MQ / MOhm)------0.6(min)-----------20 and 30(ms)

GL5528------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------10~20(kOhm)----------------1.0(MQ / MOhm)------0.7(min)-----------20 and 30(ms)

GL5537------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------16~50(kOhm)----------------2.0(MQ / MOhm)------0.7(min)-----------20 and 30(ms)

GL5539------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------30~90(kOhm)----------------5.0(MQ / MOhm)------0.8(min)-----------20 and 30(ms)

GL5549------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------45~140(kOhm)----------------10.0(MQ / MOhm)----0.8(min)-----------20 and 30(ms)