# photo sensing light switch with luxeon LED



## Tekstyle (Jan 12, 2010)

Hello there,

I am trying to build a device that turns on 2 high powered CREE-XRE LED automatically when it gets dark. I wish to add a potential or a dimmer switch so i can vary the sensitivity. I plan to use 2 18650 lithium-ion batteries to power it.

basic schematics:
a photoresistor circuit that runs off an existing 7.4v battery pack that provide me either 0 or 7.4V to a LED driver that then powers 2 CREE-XRE LED connected in parallel. I am sure there's a bunch of stuff that would go in between each step and that's where I get lost. 

To all those LED and circuit guru, your help is greatly appreciated. Thank you so much.

- Derek


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## LEDninja (Jan 12, 2010)

Make sure the light from the LEDs (direct or reflected) do not land on the photosensor. I got a 21 LED bulb and put it in an automatic electric eye nitelite. The LED bulb at 45 lumens was bright enough to fool the sensor and the combo went into strobe mode about 3 flashes per second.


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## Tekstyle (Jan 12, 2010)

LEDninja said:


> Make sure the light from the LEDs (direct or reflected) do not land on the photosensor. I got a 21 LED bulb and put it in an automatic electric eye nitelite. The LED bulb at 45 lumens was bright enough to fool the sensor and the combo went into strobe mode about 3 flashes per second.



that's interesting to know, thank you. do you think you can provide me the link to the automatic electric eye nitelite device you used? if not, would you mind me asking how much you paid for it?


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## Mark620 (Jan 12, 2010)

You could disassemble a solar light and use those parts.
Instead of the solar-light-led put in a relay.


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## bshanahan14rulz (Jan 12, 2010)

The really cheap ones use a simple 555... 

Dug up an old reverse-engineered schematic from a cheap nightlight, bottom of the case says "First Alert; Model No. FHR-2L; 120VAC 60Hz 0.3W; Made in China"

Here is the schematic. b.r.=bridge rectifier. Controlled with a photoresistor.


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## LEDninja (Jan 12, 2010)

Tekstyle said:


> that's interesting to know, thank you. do you think you can provide me the link to the automatic electric eye nitelite device you used? if not, would you mind me asking how much you paid for it?


In Canada they are available everywhere, from Dollarama, Walmart, hardware stores and drug stores. I've seen them with 7 watt incan, 1 LED and 3 LED bulbs. Prices range from $1 to $4.
21 LED bulb in manual nitelite left, automatic nitelite with electric eye right.


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## Tekstyle (Jan 13, 2010)

hey guys, thanks for all of your advices. so i stopped by a local hardware store and picked up a solar light, those used in the backyard or front porch with a solar panel on top. I took it away and i see a small board with 2 capacitors, 2 resistors, a photoresistor, 1 white LED, and 1 AA ni-cad battery. I saw the post about using a relay which i think would be the most straight forward approach in using a low current circuit to power a higher current circuit like a CREE LED. This brings me to hopefully the final part of this project which is what kind of relay and where i can get the right one.

does anyone know? mouser? digi-key?

I also read a lot about using transistors instead. I am not sure if they amplify the original signal or act like a relay by directing the flow of a higher powered flow. I am more familiar with relays than transistors since my electrical knowledge stops at the automotive level.

Since I plan on just modifying a high powered CREE LED flashlight with a photoresistor to give it the ability to turn on and off automatically when it gets dark or bright, will a 5-9v relay be ideal?


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