Nightlite circuit

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DickCappels

Joined Aug 21, 2008
10,153
@guruji , to what do you intend to connect the input of the bridge rectifier? Also, would you please post a more clear image of the schematic so we can read the values and possibly give you assistance?
 

hp1729

Joined Nov 23, 2015
2,304
Hi guys would like to know if this circuit is good cause I am trying to make ldr more sensitive without success.
Any help please?
Thanks
Component values, please.
What transistor? What photo sensor?
What resistor values?
What Zener diode?
What LED?

HP1729_nightlight.png

You can probably pick one up at the local Dollar Store a lot cheaper and safer.
 
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hp1729

Joined Nov 23, 2015
2,304
Design 762.PNG
LEDs to mains are a restricted topic, as per the Terms of Service.
Quite correct, as it should be. So ...
Will it work? Probably. Adjusting sensitivity? Not knowing anything about the light sensitive component all I can suggest is to adjust resistances until you get what you want.
Now that we have the voltage down, the transistor can be just about any NPN you have on hand. 2N3904 is cheap.
R1 - 150 or so
R3 - 220 o 1K, adjusted for desired brightness
R2 - depends or RT1
RT1 - ???
Zener - 1N751, or what ever you have on hand
Transformer - At least 50 mA, or so, what ever you have on hand or can find. Or ...
Base voltage will be V LED, + V R3 + about 600 mV = ? V
As light decreases RT1 resistance increases until "? V" is reached and the LED turns on.
What is the resistance of RT1 at that point? That gives you a value for current. Add 1 mA or so for base current. Then you know voltage and current and resistance for R2.
adjust for sensitivity.
I didn't bother to simulate or build it, but it should work.
 
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hp1729

Joined Nov 23, 2015
2,304
View attachment 106875

Quite correct, as it should be. So ...
Will it work? Probably. Adjusting sensitivity? Not knowing anything about the light sensitive component all I can suggest is to adjust resistances until you get what you want.
Now that we have the voltage down, the transistor can be just about any NPN you have on hand. 2N3904 is cheap.
R1 - 150 or so
R3 - 220 o 1K, adjusted for desired brightness
R2 - depends or RT1
RT1 - ???
Zener - 1N751, or what ever you have on hand
Transformer - At least 50 mA, or so, what ever you have on hand or can find. Or ...
Base voltage will be V LED, + V R3 + about 600 mV = ? V
As light decreases RT1 resistance increases until "? V" is reached and the LED turns on.
What is the resistance of RT1 at that point? That gives you a value for current. Add 1 mA or so for base current. Then you know voltage and current and resistance for R2.
adjust for sensitivity.
I didn't bother to simulate or build it, but it should work.
Couldn't resist. I built it.
Running from a 5 V supply ...R2 = 510, R3 = 220
Works with red or white LED, so any LED will work.
R1 depends on voltage source, figure 10 mA to 25 mA through it, or so.
RT1 on hand has about 100 ohms in bright light and >1K in dim light. Typical values.
 

boatsman

Joined Jan 17, 2008
187
I found I can run a LED headlamp (12x 5mm white LEDs) off a Nokia telephone charger (5.3v 500 mA) without any modifications. All you need is a female connection to the original male connection.
 

Thread Starter

guruji

Joined Nov 11, 2005
32
View attachment 106875

Quite correct, as it should be. So ...
Will it work? Probably. Adjusting sensitivity? Not knowing anything about the light sensitive component all I can suggest is to adjust resistances until you get what you want.
Now that we have the voltage down, the transistor can be just about any NPN you have on hand. 2N3904 is cheap.
R1 - 150 or so
R3 - 220 o 1K, adjusted for desired brightness
R2 - depends or RT1
RT1 - ???
Zener - 1N751, or what ever you have on hand
Transformer - At least 50 mA, or so, what ever you have on hand or can find. Or ...
Base voltage will be V LED, + V R3 + about 600 mV = ? V
As light decreases RT1 resistance increases until "? V" is reached and the LED turns on.
What is the resistance of RT1 at that point? That gives you a value for current. Add 1 mA or so for base current. Then you know voltage and current and resistance for R2.
adjust for sensitivity.
I didn't bother to simulate or build it, but it should work.
Hi circuit is exact. That cds is an ldr I imagined yes?
Is the zener important? what is it's function?
I did a 1meg pot instead of the 150k but still ldr not sensitive enough.
Any clue?
Thanks
 

hp1729

Joined Nov 23, 2015
2,304
Hi circuit is exact. That cds is an ldr I imagined yes?
Is the zener important? what is it's function?
I did a 1meg pot instead of the 150k but still ldr not sensitive enough.
Any clue?
Thanks
Try a smaller pot.1K or 5K.
The working range of the LDR is down in the hundreds to thousands of ohms. No, the value of the Zener is not important. It just sets the operating voltage of the rest of the circuit. 5.1 V is just a suggestion. Actually when I built the circuit I just used a 5 V power supply. No Zener or R1.
 

Thread Starter

guruji

Joined Nov 11, 2005
32
Try a smaller pot.1K or 5K.
The working range of the LDR is down in the hundreds to thousands of ohms. No, the value of the Zener is not important. It just sets the operating voltage of the rest of the circuit. 5.1 V is just a suggestion. Actually when I built the circuit I just used a 5 V power supply. No Zener or R1.
Thanks for response. Yes but zener is controlling the voltage then of the circuit cause when I removed it leds stayed on.
 

hp1729

Joined Nov 23, 2015
2,304
Thanks for response. Yes but zener is controlling the voltage then of the circuit cause when I removed it leds stayed on.
Yes, removing the Zener throws operation off unpredictably. It just doesn't have to be 5.1 Volt. A little higher would still work. You just need to adjust calibration for the changes.
 

Thread Starter

guruji

Joined Nov 11, 2005
32
Today this circuit made an explosion when connected it to mains :0
I've changred the transistor and made a 470ohm to a 4.7k pot. Don't know why maybe the transistor I chose was'nt the right one an r4001.
 

Thread Starter

guruji

Joined Nov 11, 2005
32
Hi Alec no I did not connected direct to BR. There is a 224j cap before br. I did something wrong for sure maybe switched transistor legs wrongly and blew piece of printed circuit like a fuse :(.
Regarding transistor 100hfe better than 300hfe for this circuit?
Thanks
 

Thread Starter

guruji

Joined Nov 11, 2005
32
Do you mean you're using a cap as a voltage-dropper, instead of using a transformer? If so, that's a circuit contrary to the Terms of Service!
This was made like that; a chinese nightlite circuit with a capacitive transformer. I am trying to fix it.
 
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