• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

LDR to LED's

Status
Not open for further replies.

sammy004

New Member
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.
 

audioguru

Well-Known Member
Most Helpful Member
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.
 

sammy004

New Member
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?

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

Thank You
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
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.
 

gonebush

New Member
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
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top