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Need help with photocell stats

gmontag451

Oct 10, 2021
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Oct 10, 2021
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I'm trying to choose a replacement photocell, and I'm not sure how to convert the old photocell's ratings:

1: The old cell's resistance is given at 2ft candles. I believe 2ft-candles ≈ 21 lumen, but how do I convert it to 10 lumen? Maybe (R ÷ 2.1)?

2: The old cell's Illuminated Resistance is 1.5k. But modern photocells give Illuminated Resistance as a range, like "0.5 ~ 17kOhms". How do I choose an appropriate photocell if I only have a single value?

3: How can I measure the voltage applied to the old photocell with a multimeter?

Any help would be greatly appreciated!
-Michael


The old photocell's datasheet gives the following:
Illuminated resistance 1.5k @ 2ft-candles
Min dark resistance 400k @ 2ft-candles
Max voltage 250V
 

PETERDECO

Dec 19, 2019
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Dec 19, 2019
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Welcome to the forum. I believe you are referring to an LDR (light dependent resistor). A couple of questions: what is the purpose/function of this part? Do you have a part number for the original? My LDR of choice is a 5528. It has a wide swing of resistance from 8-20K in light to a minimum of 1M dark. I have successfully used this one to replace damaged ones with unknown spec's.
 

gmontag451

Oct 10, 2021
3
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Oct 10, 2021
Messages
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Hi Peter, thank for responding and for the 5528 suggestion!
The part in question is a discontinued Clairex CL5M4 (datasheet at bottom). The circuit is used to create a flicker flame effect in an incandescent light (video). The CL5M4 is contained inside a black canister with 5 LEDs which turn on and off at different intervals, creating a random resistance. A couple of potentiometers control the min and max brightness.

I'm sure many replacement parts will work just fine, but I don't really know where to begin looking since the ratings are listed differently between the datasheet and websites like DigiKey/Mouser/etc. (Also I'm sure there are much better ways to accomplish this effect today, but the board in question has a lot of nostalgia for me!)
FFPRINT for checklist.png
 

Harald Kapp

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Nov 17, 2011
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As @PETERDECO said: go ahead, buy maybe a handful of different LDRs that fit into this position. You have two potentiometers to adjust the circuit and match the behavior to the LDR:
upload_2021-10-12_6-40-22.png
LDRs are not very precise components, their parameters can vary widely. And with the two potentiometers I'm confiident you can adjust the behavior of the circuit to your liking.
 

gmontag451

Oct 10, 2021
3
Joined
Oct 10, 2021
Messages
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Thanks for the advice! I kind of expected this would be the case, but I didn't have the experience with these to take that leap. Glad you guys were here! I've posted the same in 5 different forums and received no responses anywhere else, so thank you.
 
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