Circuit to allow triac/bridge rectifier based ac controller circuit with manual potentiometer control to be controlled by PWM

Thread Starter

besligar

Joined Mar 9, 2023
28
It is better to use this pair:

LDR: Light Dependent Resistor NSL 4960, 1 MΩ -->500 Ω, 500 mW, 320 V, 550 nm (peak).
LED: Super-Green LED (GaInN/GaN) RL5-G5023 3.5 V, 20 mA, 5000 mcd, 524 nm (peak).
So if you've been following the thread you will know I know very little about these, thanks for the suggestion of these two, Can you explain why? The kit I ordered above will give a great assortment for playing with and experimenting so no regrets on that but I'm sure I'm missing something regarding this project and what I'm looking to do. Since you pointed out some specs I got looking at my list and I see Response Time Rose and Drop - .6(min). Does that mean 36secs for a full rise AND drop or 16 secs for a full rise OR drop? I see the LDR you listed is $11.50 so is response time and light sensitivity a lot better?
 

Thread Starter

besligar

Joined Mar 9, 2023
28
That certainly is a lot of LDRs, and depending on the size you may be able to have two of them illuminating the one you use. If the PWM voltage is 5 volts then you can use two in series and no resistor will be required, unless you intend to run 100% duty cycle all the time. I am guessing that minimum resistance is maximum speed, but maybe not.
If you need more light then the PWM could drive the base of a single NPN transistor that you might have, or would cost you perhaps 25 cents for one. and that transistor could switch 5 volts at 100 milliamps or more, enough current to drive several standard LEDs, or one high powered one, with a resistor.
If you look at them on Amazon it's like 50 or 200 for $10 or $12 of the same part. One review I read the guy got 200 but they varied widely in range....but with 200 to play with he could sift through them to get what he wanted. Farther down I found this kit which seems like a lot more reasonable way to go, 25 each of the seven common sizes.
 

MisterBill2

Joined Jan 23, 2018
18,167
So if you've been following the thread you will know I know very little about these, thanks for the suggestion of these two, Can you explain why? The kit I ordered above will give a great assortment for playing with and experimenting so no regrets on that but I'm sure I'm missing something regarding this project and what I'm looking to do. Since you pointed out some specs I got looking at my list and I see Response Time Rose and Drop - .6(min). Does that mean 36secs for a full rise AND drop or 16 secs for a full rise OR drop? I see the LDR you listed is $11.50 so is response time and light sensitivity a lot better?
No, that "6" is the sensitivity rating. The rise and fall times are in milliseconds, 30 to40 for some. That will provide a filter to avoid the PWM frequency from causing problems.
 

Danko

Joined Nov 22, 2017
1,829
So if you've been following the thread you will know I know very little about these, thanks for the suggestion of these two, Can you explain why? The kit I ordered above will give a great assortment for playing with and experimenting so no regrets on that but I'm sure I'm missing something regarding this project and what I'm looking to do. Since you pointed out some specs I got looking at my list and I see Response Time Rose and Drop - .6(min). Does that mean 36secs for a full rise AND drop or 16 secs for a full rise OR drop? I see the LDR you listed is $11.50 so is response time and light sensitivity a lot better?
LDR:
500 mW , 320V - than higher power, than better thermostability; higher voltage - better reliability.
1 MΩ - should be much more than desirable 200k, then LDR becomes faster.
LED:
5000 mcd - than more luminous intensity than wider dynamic range of photocoupler.
524 nm (peak) - should be close to spectral peak of LDR for maximal sensitivity.

Below is example diagrams, showing LDR inertia - rise and drop durations (PWM 5V, 20kHz, 1% - 99%):

1679840357158.png_1679835463851.png
 
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Thread Starter

besligar

Joined Mar 9, 2023
28
Just a little update, I've been playing with the kit of LDR's and there seems to be promise in this method. Thanks for your info DanKo, it makes more sense working with these now.
They aren't marked individually so you pretty much want to test them to know what you're working with. The instant you put a piece of shrink wrap over them and pinch the open end they want to climb considerably above the anticipated value. But once in operation the very first light seems to bring them around the anticipated max ohm level and it goes down from there with more light.
Using a PWM generator it worked fairly well but not a linear movement.
When hooked up to Mach3 with tach input it will work it's way to the set speed but does a lot of hunting to get there. Obviously the PID settings will come into play there so more experimenting to do. Depending on your end use and the controller used to issue the PWM this could be an option.
Pictures below on how I went about this, the shrink wrapping technique was discussed on another website.
 

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MisterBill2

Joined Jan 23, 2018
18,167
I remind you that LED devices are rather non-linear, and probably the LDR devices are also not perfectly linear. BUT they ARE rather repeatable. And using LEDs of different colors may also affect the response.
 
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