Wrong LDRs?

tablebeast

tablebeast

Member
I bought two LDRs from Pedal PCB recently for my Delegate Compressor (Boneyard Edition) build. I ordered two "GL5516 LDR Photo Resistor", which is supposed to be 5 – 10K light, 500K dark. Well, I did not get those parts. I got two different parts and BOTH were wrong. One was like 2k light, 50k dark and the other was 0 light and 5M dark. Neither will work correctly with my circuit. I thought ordering two of them would make sure one worked out correctly, but I was wrong. -EDIT-
 
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Locrian99 said:
Did you attempt to message him a 2nd time after no response. He is one guy and I can tell you at my work. Ive missed an email or two before.

Also how did you test the ldr’s?

I’m sure robert will get you taken care of
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I tested them with a multimeter and measured the resistance in the dark and with an LED shoved in its face. Of course I DIDN'T test before I built, trusting that the part I ordered was actually the correct one. My mistake there. When the compressor worked like crap, I took the LED/LDR pair I had shrink-tubed off the board and tested the resistance. Then I tested my "backup" part the same way. Both were wildly off in different directions. So neither were the correct part.

Sorry I had to call it out like this on the forum. I just wanted to make sure there wasn't a larger issue going on. Thanks for the responses.
 
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You didn't get incorrect parts. There's a lot of variation in cheap LDRs. It's one of those parts where it you want a Goldilocks value, you need to get 10-20 and cherrypick.
There's also some manual tuning to be done. Brightness of LED, spacing and axis orientation all affect response.
You may be able to get the 5M one to work with a dimmer led and slightly off axis/higher spacing.
Make sure you check out Chucks thread on the mods he did to this.
 
Hmmmm, I make a fair few of these. I buy maybe 30 5516s at a time as they go in some other pedals I build. I get them from whoever has the best deal, on eBay generally in the UK. Iv never tested one ever, and I have never had an issue.

Grab 10 or so from somewhere if your intent on getting something right on speck, but you do have to have perfect conditions to test properly - they are cheep. I am sure Robert will come back to you.

Just my 10p worth
 
ac30irons said:
Hmmmm, I make a fair few of these. I buy maybe 30 5516s at a time as they go in some other pedals I build. I get them from whoever has the best deal, on eBay generally in the UK. Iv never tested one ever, and I have never had an issue.

Grab 10 or so from somewhere if your intent on getting something right on speck, but you do have to have perfect conditions to test properly - they are cheep. I am sure Robert will come back to you.

Just my 10p worth
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Yea ive never had an issue with them don’t think I’ve ever measured them. I am going to go out on a limb here and guess the ldr isn’t the problem. I get the impression that won’t be taken well as a suggestion lol
 
I'm going to chalk up the lack of response not to being ignored, but more likely an online form that never was actually sent, even though it said "thanks for sending" when I clicked it. Robert got RIGHT back to me when I direct messaged him. Thanks for clearing up the confusion, sir. But now I'm wondering how wildly these parts differentiate. One had a max resistance of 50k and the other was over 5M. Thats not close to the 500k I need at all. I'll try the two he sends me, but I may need to get a pile of them and cherry pick. Thanks for the quick resolution, in any case.
 
The test procedures for LDR's are very specific. From the data sheet of the GL5516:

"Dark resistance: Refer to the resistance ten seconds after the 10Lux light is shut up (sic)."

10 Lux is a very low dim amount of light

From Chuck's build report:

I used a frosted white LED. It's very bright even at low current. It turned out to be overkill. The LDR I used is in a TO-18 can, obtained from Electronic Goldmine. They were dirt cheap on sale, like 40 cents each. One ot two stinkers in the bunch, but the rest went from under 2K (illuminated) to over 2Meg (dark). Cadmium Sulfide LDRs have a quick response to light, their resistance drops in a few milliseconds. Their response to dark is much slower, over 100ms to get from 2K to 500K. The more light that hit them, the longer it takes for the resistance to go up. That's why a bright LED isn't always a good thing. I find it best to set the ATTACK at 8:00 or 9:00 so the peak LED current is less and the release is quicker.


If your test procedure involves anything but a dark room and the soft glow of a distant 15w light bulb, your readings are likely to be inaccurate, which is the source of your problem.


Also, Chuck mentions the specs for his LDR's, which are different from the GL5516, and they still work fine. You should try what you have and see if you like the pedal as a whole.
 
PM sent, I'll get another set shipped out to you tomorrow morning.

Locrian99 said:
Also how did you test the ldr’s?
Click to expand...

This is important. The resistances listed in the datasheet are taken under very specific circumstances.

According to the datasheet light resistance is measured "at 10 Lux with standard light (2854K color temperature) and 2hr illumination at 400-600 lux prior to testing".

Dark resistance is a guaranteed minimum. If the dark resistance is spec'd at 500K that doesn't mean the LDR is going to stop dead on 500K, it means it is guaranteed to at least measure 500K, and "Measured 10 seconds after closed 10 lux."

The resistance can continue to increase far beyond the listed maximum, it's just guaranteed to be at least that much after 10 seconds.
 
Locrian99 said:
Yea ive never had an issue with them don’t think I’ve ever measured them. I am going to go out on a limb here and guess the ldr isn’t the problem. I get the impression that won’t be taken well as a suggestion lol
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The light and the resistor might as well be the whole compressor. Its what tells the thing what to compress, when, and for how long. It absolutely matters. I've used these types of LDRs before in other applications and I'm well aware of how they work and how to test them. These are different parts and they don't match what I need. Upon testing they gave VERY different results with the same LEDs. I tried several kinds just to be sure. Of course I got different readings with the various LED types, but they were both still way off of what I needed. I did figure out that the diffused green is a better choice than the bright white, but no combination is going to make up for the maximum resistance being off by an order of magnitude in either direction.
 
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