LED project

[gqma0]

Hi all.

I need to automatically light up a hall during night time for my 2 young kids who get out of bed in the middle of the night to go to the toilets
I have no AC sockets in the hall located in the middle of the house.

Basically, I have a bunch of White Ultrabright leds (3V). 1 LED (8000 mcd) is powerful enough to brighten the hall and they don't consume much power. I also have 2 solar panels (1.5v 135ma) and a LDR (77k-340k)

The plan is to use the existing components and the following circuit based on a 3V input with 2 x NiMH batteries (1200mah)

**broken link removed**

The Solar cells would be placed on the window (in my daughters room) facing south
The LED would light up when near darkness is happening.

But I'm not too sure which NPN transistor I should be Choosing and which value for the resistors.

Can you point me in the right direction ? I'm just starting in electronics

Thanks
G

 

[Ubergeek63]

first, NiMH do not like to be float charged or overcharged, take a look at LiFePO:
**broken link removed**

second, whites will not work in that circuit since they require 3.5V give or take to reach full brightness.

you will need a boost current source to run them.

 

[gramo]

Can you run two wires along the skirting? This is all you would need for your LED's from the circuit...

You don't need much current to brighten things up at night with LED's, so the wire does not need to be hefty

 

[audioguru]

First you should try a $3.00 solar garden white light on the window ledge in your daughter's room. In shade behind glass it might charge its battery enough to light dimmly for 10 minutes each night.

Use a 6VDC wall wart AC adapter in your daughter's room to power the LED or LEDs in the hall through your transistor circuit.

 

[gqma0]

At the moment, I have 2 ultrabright LEDs in // powered by 2xAA to brighten the hall at night. The light intensity is sufficient enough. Not looking for the best light result

I checked the voltage (2.94v) and current (0.8ma) for 1 LED


Ubergeek63, thanks for that, I will take that in consideration

gramo, I plan to run the wires in the my daughter's room coving then through the drywall. I have cheap audio speakers that I never used which will do for the project. I also plan to run a wire in the ceiling to bring a LED over the toilet in the bathroom.

Unfortunately, the solar garden lights are expensive here in Ireland (€8, around $12) + I already have solar cells. Also, there are too many bulky DC adapters in the house (Cordless phone, cell phone, Baby monitor, etc...) I'm trying to be eco friendly here and save energy.

Thanks
G

 

[audioguru]

Your two AA alkaline cells are 3.0V when new. Their voltage will quickly drop to 2.4V then the 3V white LEDs won't light anymore.
If you use three AA cells in series to make 4.5V when they are new then use a current-limiting resistor in series with the two paralleld LEDs, they will still light pretty well when the 4.5V battery drops to 3.6V.
For 20mA in each LED the resistor should be (4.5V - 3.0V)/40mA= 37.5 ohms which is not a standard value. Use 39 ohms.

 

[gqma0]

Thanks audioguru for the information. I will suplly with 3 cells then.