LDR to LED's

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sammy004

New Member

• Jun 2, 2009

• #1

Hi guys can some please help me out, I wanted to know how I can connect 4 White LED's to a LDR the simplest way possible I don't know that much about electronics so please tell me dummy terms. I want it to turn on the LED's at night and off at day and I will have it hooked up to a 9volt battery. I will really appreciate anyones help.

 

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Jony130

Active Member

• Jun 2, 2009

• #2

You can uses this kind of circuit.
It is a Schmitt trigger

 

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sammy004

New Member

• Jun 2, 2009

• #3

wow that looks complicated I was hoping for something a lot simplier.

 

Sceadwian

Banned

• Jun 2, 2009

• #4

https://www.electro-tech-online.com/threads/555-dark-detector-circuit-help.33245/

It's a bit simpler.

 

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Jony130

Active Member

• Jun 2, 2009

• #5

There's nothing simpler than this circuit

 

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audioguru

Well-Known Member

Most Helpful Member

• Jun 2, 2009

• #6

A 9V alkaline battery will be dead in about 8 hours with a 40mA load. 7V of the 9V is wasted in heating the resistors.
If four AA alkaline battery cells are in series making 6V then they can power 40mA for about 40 hours.

 

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sammy004

New Member

• Jun 2, 2009

• #7

Thank you everyone for helping me out I really appreciated everyones advice so quickly. I kinda like this idea

And is that a 47K Pot? what is that for?

audioguru said:

A 9V alkaline battery will be dead in about 8 hours with a 40mA load. 7V of the 9V is wasted in heating the resistors.
If four AA alkaline battery cells are in series making 6V then they can power 40mA for about 40 hours.

Click to expand...

I don't get it 6V will last longer than 9V, Can you please explain how that will work?

Thank You

 

Last edited: Jun 2, 2009

audioguru

Well-Known Member

Most Helpful Member

• Jun 3, 2009

• #8

I just realized that you are lighting 3.5V white LEDs instead of 2V red LEDs.
The voltage does not matter since 5.5V of a 9V battery is wasted heating the resistors instead of lighting the LEDs. 6V is better since not as much voltage is wasted and the LEDs will still light when the 6V battery drops to 4v when it is almost dead.

AA cells are almost 5 times bigger than the tiny AAAA cells in a 9V battery so they provide the current for almost 5 times longer.

 

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gonebush

New Member

• Jul 20, 2009

• #9

Can somebody help me on with this this is part of the circuit that I want to build but want it to flash as well (about every 2 to 3 seconds. thanks

 

Hero999

Banned

• Jul 20, 2009

• #10

Simple, use a flashing LED.
**broken link removed**