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I want to know whether I am doing is right or wrong. I first created a 3 White LED setup with 142 ohm resistor. I am going to do similar kind of sets like 5 rows or 10 rows of 3 LEDs each. Should I use 142 ohm for each row or is it going to be different ?

Also I want to create these kind of LED setup using AC power. Instead of using AC-DC adapter is there any kind of small transformer which I can connect to it.

Buy a 220v to 12 v transformer(should cost around Rs:30) and add a bridge rectifier circuit to get 12 to 14 DC.

Below is a pic of the transformer with the bridge rectifier circuit.
The green wires are input(220v AC), the purple wires are output(12v AC) and the bridge rectifier rectifies the 12v AC to 12v DC.


Bridge rectifier schematic:


Diodes - 1N4001 (4nos)
Electrolytic capacitor- 1000mf/35 or 40volts (1 no[s])

Pic source:XCircuit Schematic Capture Tutorial Page

Thanks BBS, I will try this out.

Any idea about my other question, setting up 10 Rows of LEDs. The LED calculator says 14 ohms 8 Watt. Should I use 14 ohms for each row of 3 LEDs ?

gopinathann, that circuit is exactly the same as what is used in adaptors. so if you find it hard to make/get an adapter cheaper, stick with the adaptor

the resistance value seems strange. I'd say 150 ohm resistor in series with 3 LED's in series, and wire 10 of these in parallel :)

Your comment seems to be correct. For the following circuit 150 ohms is the correct value, however I am not sure how other calculator gives those strange values.
Input Voltage : 13
Forward Current: 3.3
Desired Current: 25 mA

if this lamp will be run mostly on battery (~12V) and for short durations, you can use 100 ohms

On the other hand , if this is going to be used with the engine on (14.4V) , and a lot of the time , try going even higher, say 180/220 ohms - My numberplate lights have begun to die out - and this is the 2nd time in 4 months, so am planning to increase the resistance to 220.

Am sick and have been advised bed rest, + my soldering iron is dead, So my plans will be on hold for a while :(

Good work. It all worth the effort made!
Cheers!

Thanks Greenhorn, I ll change the setup soon and add the resistor. What value of resistor should for my present setup?

What are these LEDs called? how much do they cost?stupid:





BTW, here is the pic of the same



Uh Oh, take care greenhorn, hope you recover soon.

and you appear online on TBHP early morning??

Thats a perfect TBHP Maniaclap:

srikant, add a 100 ohm resistor in series with each row of 3 led's , and then put them in parallel, like in gopinathann's pic above

Hi,

I tried putting 3 LED's in series with a 100 ohms resistor for the boot lamp and tested the circuit on a 5V adapter. The LED's would not glow but the same setup if made parallel would emit very good light...

Is it something that the current being 5V is inadequate for the 3 LED's in series since I guess each LED's takes around 3-3.5 V. However i have not tried this on a 12V setup.

I am doing the setup tonite by soldering the LED's on a PCB. Any reply before that would be really helpful..Anyways..i am thinking of trying out the same (series) setup on a 12V source..

Regards,

Rahul.

rahul, you're thinking along the right lines :)

if you have one of them breadboards, try it out on that before soldering

and make sure you get the polarity right while soldering the LED's :)

3 L.E.D. in series with a 100ohm or 150ohm resistor would work fine on a 12v source and not on 5volts.

I am surprised to see that the White LED doesn't glow on a 1.5 v battery but the normal bulb glows. Atleast the LED should show some light when connected to a battery. I have a torch which has 6 LEDs and runs on a single battery.

the torches have LED Driver IC's inside which step up the voltage. We dont have that luxury :D

I have a transparent LCD clock which runs on single AAA battery. I want to use the same battery to throw some light on it in the night. Which LED should I use for this ?